Temporal Instant

Configure temporalInstantChrono with timezone and fractionalDays directly in the scheduler config, for example config: { ...modelConfig, timezone: 'Asia/Tokyo', fractionalDays: false }. Both fields can be omitted to use defaults ('UTC' and false). Direct calls require the complete configuration: temporalInstantChrono.create({ config: { timezone: 'Asia/Tokyo', fractionalDays: false } }). Scheduler creation validates configuration and supplies defaults.

With fractionalDays: false, difference counts calendar days in the configured timezone. With true, it includes fractions of a day in that timezone. add uses fixed 24-hour days for UTC and calendar days for other timezones; across daylight-saving transitions, a local day can be shorter or longer than 24 hours. Fractional additions use the length of the adjacent local day. This preset does not implement a custom daily rollover hour.

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Install temporal-polyfill in your application. The example imports its global entry point before creating the Chrono; it installs Temporal in the executing runtime only when native Temporal is unavailable. The second import supplies global TypeScript declarations.

npm

yarn

pnpm

bun

deno

npm install temporal-polyfill

import 'temporal-polyfill/global'
import 'temporal-polyfill/types/global'
import { const temporalInstantChrono: Chrono<{
    readonly time: SRSSchema<{
        input: Temporal.Instant;
        output: Temporal.Instant;
    }>;
    readonly config: SRSSchema<{
        input: {
            readonly timezone?: string | undefined;
            readonly fractionalDays?: boolean | undefined;
        };
        output: {
            readonly timezone: string;
            readonly fractionalDays: boolean;
        };
    }>;
    readonly fields: {
        readonly card: SRSSchema<{
            input: {
                dueAt: Temporal.Instant;
                lastReviewAt?: (Temporal.Instant | null) | undefined;
            };
            output: {
                dueAt: Temporal.Instant;
                lastReviewAt: Temporal.Instant | null;
            };
        }>;
        readonly revlog: SRSSchema<{
            input: {
                dueAt: Temporal.Instant;
                lastReviewAt?: (Temporal.Instant | null) | undefined;
                reviewTime: Temporal.Instant;
            };
            output: {
                dueAt: Temporal.Instant;
                lastReviewAt: Temporal.Instant | null;
                reviewTime: Temporal.Instant;
            };
        }>;
    };
}>
temporalInstantChrono } from 'ts-fsrs'

const const clock: ChronoCore<Temporal.Instant>clock = const temporalInstantChrono: Chrono<{
    readonly time: SRSSchema<{
        input: Temporal.Instant;
        output: Temporal.Instant;
    }>;
    readonly config: SRSSchema<{
        input: {
            readonly timezone?: string | undefined;
            readonly fractionalDays?: boolean | undefined;
        };
        output: {
            readonly timezone: string;
            readonly fractionalDays: boolean;
        };
    }>;
    readonly fields: {
        readonly card: SRSSchema<{
            input: {
                dueAt: Temporal.Instant;
                lastReviewAt?: (Temporal.Instant | null) | undefined;
            };
            output: {
                dueAt: Temporal.Instant;
                lastReviewAt: Temporal.Instant | null;
            };
        }>;
        readonly revlog: SRSSchema<{
            input: {
                dueAt: Temporal.Instant;
                lastReviewAt?: (Temporal.Instant | null) | undefined;
                reviewTime: Temporal.Instant;
            };
            output: {
                dueAt: Temporal.Instant;
                lastReviewAt: Temporal.Instant | null;
                reviewTime: Temporal.Instant;
            };
        }>;
    };
}>
temporalInstantChrono.Chrono<{ readonly time: SRSSchema<{ input: Temporal.Instant; output: Temporal.Instant; }>; readonly config: SRSSchema<{ input: { readonly timezone?: string | undefined; readonly fractionalDays?: boolean | undefined; }; output: { readonly timezone: string; readonly fractionalDays: boolean; }; }>; readonly fields: { readonly card: SRSSchema<{ input: { dueAt: Temporal.Instant; lastReviewAt?: (Temporal.Instant | null) | undefined; }; output: { dueAt: Temporal.Instant; lastReviewAt: Temporal.Instant | null; }; }>; readonly revlog: SRSSchema<{ input: { dueAt: Temporal.Instant; lastReviewAt?: (Temporal.Instant | null) | undefined; reviewTime: Temporal.Instant; }; output: { dueAt: Temporal.Instant; lastReviewAt: Temporal.Instant | null; reviewTime: Temporal.Instant; }; }>; }; }>.create: (ctx: {
    readonly config: {
        readonly timezone: string;
        readonly fractionalDays: boolean;
    };
}) => ChronoCore<Temporal.Instant>
create({
  config: { timezone: 'America/New_York', fractionalDays: false },
})
const const fractionalClock: ChronoCore<Temporal.Instant>fractionalClock = const temporalInstantChrono: Chrono<{
    readonly time: SRSSchema<{
        input: Temporal.Instant;
        output: Temporal.Instant;
    }>;
    readonly config: SRSSchema<{
        input: {
            readonly timezone?: string | undefined;
            readonly fractionalDays?: boolean | undefined;
        };
        output: {
            readonly timezone: string;
            readonly fractionalDays: boolean;
        };
    }>;
    readonly fields: {
        readonly card: SRSSchema<{
            input: {
                dueAt: Temporal.Instant;
                lastReviewAt?: (Temporal.Instant | null) | undefined;
            };
            output: {
                dueAt: Temporal.Instant;
                lastReviewAt: Temporal.Instant | null;
            };
        }>;
        readonly revlog: SRSSchema<{
            input: {
                dueAt: Temporal.Instant;
                lastReviewAt?: (Temporal.Instant | null) | undefined;
                reviewTime: Temporal.Instant;
            };
            output: {
                dueAt: Temporal.Instant;
                lastReviewAt: Temporal.Instant | null;
                reviewTime: Temporal.Instant;
            };
        }>;
    };
}>
temporalInstantChrono.Chrono<{ readonly time: SRSSchema<{ input: Temporal.Instant; output: Temporal.Instant; }>; readonly config: SRSSchema<{ input: { readonly timezone?: string | undefined; readonly fractionalDays?: boolean | undefined; }; output: { readonly timezone: string; readonly fractionalDays: boolean; }; }>; readonly fields: { readonly card: SRSSchema<{ input: { dueAt: Temporal.Instant; lastReviewAt?: (Temporal.Instant | null) | undefined; }; output: { dueAt: Temporal.Instant; lastReviewAt: Temporal.Instant | null; }; }>; readonly revlog: SRSSchema<{ input: { dueAt: Temporal.Instant; lastReviewAt?: (Temporal.Instant | null) | undefined; reviewTime: Temporal.Instant; }; output: { dueAt: Temporal.Instant; lastReviewAt: Temporal.Instant | null; reviewTime: Temporal.Instant; }; }>; }; }>.create: (ctx: {
    readonly config: {
        readonly timezone: string;
        readonly fractionalDays: boolean;
    };
}) => ChronoCore<Temporal.Instant>
create({
  config: { timezone: 'America/New_York', fractionalDays: true },
})

// Noon in New York, the day before daylight saving time starts.
const from = Temporal.Instant.from('2026-03-07T17:00:00Z')
const next = const clock: ChronoCore<Temporal.Instant>clock.ChronoCore<Temporal.Instant>.add: (from: Temporal.Instant, days: number) => Temporal.Instantadd(from, 1)
const halfDay = const clock: ChronoCore<Temporal.Instant>clock.ChronoCore<Temporal.Instant>.add: (from: Temporal.Instant, days: number) => Temporal.Instantadd(from, 0.5)

console.log(
  JSON.stringify(
    {
      nextDayUTC: next.toString(),
      elapsedHours: from.Temporal.Instant.until(other: Temporal.InstantLike, options?: Temporal.RoundingOptionsWithLargestUnit<Temporal.TimeUnit>): Temporal.Duration (+1 overload)until(next).Temporal.Duration.total(totalOf: Temporal.PluralizeUnit<Temporal.DateUnit | Temporal.TimeUnit>): number (+3 overloads)total('hours'),
      calendarDays: const clock: ChronoCore<Temporal.Instant>clock.ChronoCore<Temporal.Instant>.difference: (from: Temporal.Instant, to: Temporal.Instant) => numberReturns the distance from the previous review time to the current time.difference(from, next),
      fractionalDays: const fractionalClock: ChronoCore<Temporal.Instant>fractionalClock.ChronoCore<Temporal.Instant>.difference: (from: Temporal.Instant, to: Temporal.Instant) => numberReturns the distance from the previous review time to the current time.difference(from, halfDay),
    },
    null,
    2
  )
)

March 7 at noon in New York is 17:00 UTC. Adding one local calendar day reaches March 8 at noon, or 16:00 UTC: only 23 hours have elapsed because daylight saving time has started. fractionalDays: true measures the half-day addition as 0.5.

#Temporal Instant

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Temporal Instant

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