2. Use the Time-Provider API

Compat keeps the native call shapes. The Time-Provider's own API reads better: delays are durations instead of milliseconds, a handle cancels itself with dispose(), and there are primitives with no native counterpart (wait, recurring, cron). Rewrite one call at a time; both styles run on the same timers.

Compat	Time-Provider API
compat.setTimeout(fn, 5_000)	scheduler.timers.once({ seconds: 5 }, fn)
compat.setTimeout(fn, 5_000, a)	scheduler.timers.once({ seconds: 5 }, () => fn(a))
compat.setInterval(fn, 60_000)	scheduler.timers.every({ minutes: 1 }, fn)
compat.clearTimeout(h), compat.clearInterval(h)	h.dispose()
compat.queueMicrotask(fn)	scheduler.microtasks.queue(fn)
compat.requestAnimationFrame(fn)	scheduler.animation.scheduleFrame(fn)
compat.requestIdleCallback(fn, { timeout: 1_000 })	scheduler.idle.request(fn, { timeout: 1_000 })
compat.cancelAnimationFrame(h), compat.cancelIdleCallback(h)	h.dispose()
compat.performance.now()	clock.monotonicNow()
compat.performance.timeOrigin	clock.monotonicOrigin
compat.performance.mark("a")	timings.mark("a")
compat.performance.measure("a-b", "a", "b")	timings.measure("a-b", { start: "a", end: "b" })
compat.performance.getEntriesByName("a")	timings.entries({ name: "a" })
compat.performance.getEntriesByType("mark")	timings.entries({ kind: "mark" })
compat.performance.clearMarks("a")	timings.clear({ kind: "mark", name: "a" })

Every member hangs off timeProvider. See the API reference for the full signatures.

Dates

Date never went through compat, so it moves here straight from the native call. utcNow() and localNow() return the plugin's own date type: a Date with plugin-native, a Day.js object with plugin-dayjs, and so on.

Native	Time-Provider API
Date.now()	clock.timestampNow()
new Date()	clock.utcNow()
dayjs(), DateTime.now(), moment()...	clock.localNow(), on a timezone-aware plugin

Patterns that get simpler

A promise around setTimeout

Compat

await new Promise<void>((resolve) => timeProvider.compat.setTimeout(resolve, 2_000));

Time-Provider API

await timeProvider.scheduler.timers.wait({ seconds: 2 });

A setTimeout that reschedules itself

Compat

let delay = 1_000;
const retry = () => {
  if (trySend()) return;
  delay *= 2;
  timeProvider.compat.setTimeout(retry, delay);
};
timeProvider.compat.setTimeout(retry, delay);

Time-Provider API

let delay = 1_000;
timeProvider.scheduler.timers.recurring(
  () => (trySend() ? false : { milliseconds: (delay *= 2) }),
  { milliseconds: delay },
);

recurring returns one handle for the whole chain, so one dispose() stops it.

Cancelling with an AbortSignal

Compat

const handle = timeProvider.compat.setTimeout(save, 5_000);
signal.addEventListener("abort", () => timeProvider.compat.clearTimeout(handle));

Time-Provider API

timeProvider.scheduler.timers.once({ seconds: 5 }, save, { signal });

Keep dates out too

Once a folder reads its dates from the clock, extend the ESLint config from step 1 with two rules that still allow new Date(value):

"no-restricted-properties": ["error", { object: "Date", property: "now" }],
"no-restricted-syntax": ["error", "NewExpression[callee.name='Date'][arguments.length=0]"],

Drop the compat addon when nothing calls it any more.