Public appointment booking screen fails to show time slots with some timezones

[SebastianKrupinski]

Steps to reproduce

1. Configure appointment booking in Calendar. (15min slots in American/Toronto timezone)
2. Open appointment booking using link.
3. Change appointment time zone to American/Vancover

American/Toronto timezone

American/Vancover timezone

Expected behavior

Time zones are only 3 hours apart some slots should still be visible.

Actual behaviour

No time slots displayed

Calendar app version

4.8.0-alpha.1

CalDAV-clients used

N/A

Browser

Brave 1.64

Client operating system

Windows

Server operating system

No response

Web server

Nginx

Database engine version

MariaDB

PHP engine version

PHP 8.2

Nextcloud version

28.0.4

Updated from an older installed version or fresh install

None

List of activated apps

No response

Nextcloud configuration

No response

Web server error log

No response

Log file

No response

Browser log

No response

Additional info

No response

[SebastianKrupinski]

This seems to only happen for certain dates.

Toronto TZ - Monday (Home Time Zone)

Vancouver TZ - Monday (4 Hours difference)

Vancouver TZ - Tuesday (4 Hours difference)

Appointment Booking Settings (Toronto TZ)

[hbarel]

Same here. Timezone differences are off by one extra hour.

[hbarel]

Moreover, when switching between time-zones at the booking selection screen, even the number of available slots changes dramatically (e.g., from 10 in one timezone to 2 in another).