A pilot, soak test or canary window is a slice of the year — and the year has its own rhythm. Drag the window across recurring ops events and see which it actually catches, which it clips, and which fire entirely outside it. The third leg of the burn-in question (kindCoverage of the input space — how much variety has the system already seen. · rateTraffic rate — how many trials in the window, from rule-of-three or Clopper–Pearson. · time).
The window
Burn in fordays starting.
Looking at 2026 — May 26 → Jun 9. 0 of 10 events fully caught, 1 partial, 9 missed (1 doesn't fire this year).
The year, with your window on it caught partial / once missed n/a this year
JanFebMarAprMayJunJulAugSepOctNovDec
Month-end close1/12
Mid-month payroll / billing0/12
Quarter-end close0/4
Year-end freeze0/1
Black Friday & Cyber Monday0/1
Leap day—
US DST spring-forward0/1
US DST fall-back0/1
EU DST spring-forward0/1
EU DST fall-back0/1
Tax / VAT year boundary0/1
Drag the band to move; pull either edge to resize.
Never fires in the window: Mid-month payroll / billing, Quarter-end close, Year-end freeze, Black Friday & Cyber Monday, US DST spring-forward, US DST fall-back, EU DST spring-forward, EU DST fall-back, Tax / VAT year boundary.
Only fires once — n = 1 isn't a sample: Month-end close.
Doesn't fire in 2026: Leap day.
To catch more:
Extend by 6 days at the end → catches Mid-month payroll / billing.
Extend by 21 days at the end → catches Quarter-end close.
Extend by 57 days at the start → catches EU DST spring-forward.
Catalog — prune what isn't yours
Books close on the last day of each month — finance posts, reports run.
Pay runs and recurring bills concentrated on the 15th.
Last three days of Mar / Jun / Sep / Dec — heavier than a normal month-end.
The holiday change-freeze: skeleton crew, batch jobs still running.
Thu–Mon around the US Thanksgiving weekend — peak retail traffic.
Feb 29 — fires every fourth year. The classic blind spot.
2nd Sunday of March: clocks jump 02:00 → 03:00 in US/Canada.
1st Sunday of November: 02:00 happens twice in US/Canada.
Last Sunday of March: clocks jump 01:00 → 02:00 UTC across the EU.
Last Sunday of October: 01:00 UTC happens twice across the EU.
Jan 1: rate tables, fiscal calendars and invoice numbering all roll over.
Your own events
Add the one-offs and quirks that aren't generic — your cert rotation, your VAT-table reload, the launch you're protecting.
Calendar-year strip wraps at Dec 31 — a window crossing the boundary shows as two arcs, since recurring events care about month-day, not which year.