Cron monitor timezones not using daylight saving time adjustment

[DaveHasteSpringer]

Environment

SaaS (https://sentry.io/)

Steps to Reproduce

1. During non-DST (i.e. before 10th March 2024), configure a cron monitor on a schedule specified in the America/New_York timezone
2. Observe the monitor running at the correct schedule for that timezone (i.e. EST)
3. Wait until DST comes into effect (i.e. 10th March 2024)
4. Observe that the monitor runs at an incorrect time: one hour early in EDT (which is now the correct timezone for America/New_York)

Expected Result

I would expect the cron monitor to continue run at the configured time, taking Daylight Saving Time adjustments into account.

Actual Result

In February I set up a monitor to run daily at 07:00 in the America/New_York timezone (which was EST at the time). It ran on schedule, as expected.

A few days ago, New York moved into DST (Daylight Saving Time), so the local time became EDT (i.e. no longer EST). Unexpectedly, the monitor doesn't seem to take the move to DST into account, so it now runs at 06:00 EDT, which is incorrect.

The attached screenshots from the Sentry web UI show that the configuration is specified correctly, but that an issue was raised one hour too early.

Config (correct):

Issue raised (incorrect):

Product Area

Crons

Link

https://springernature.sentry.io/crons/eus-weeknight-startup/

DSN

No response

Version

No response

[getsantry]

Assigning to @getsentry/support for routing ⏲️

[getsantry]

Routing to @getsentry/product-owners-crons for triage ⏲️

[evanpurkhiser]

Hi @DaveHasteSpringer -- Is it continually reporting these since the timezone change on March 10th? I assume yes since in your screenshot I see it was reported this morning.

[evanpurkhiser]

Oh, I see, your schedule declares that today would have been the first day after the timezone change.

Let me investigate further. I suspect the computation for the next check-in may be failing to fully consider timezones.

[DaveHasteSpringer]

@evanpurkhiser It seems that this problem manifested itself for two consecutive days (from 10th March onwards), for all of the cron monitors we have set up in the New York timezone.

However, as of last night, I can see that some of the cron monitors that we have in that timezone have started running at the correct time.