Issue Summary

Confluence Team Calendars: unable to save events that include non-existent DST times (e.g. 12:00 AM–2:00 AM on 29 March 2026 in DST-affected time zones). Clicking "Save" briefly shows a spinner, the dialog stays open, no error is displayed, and the event is not created or updated.

Steps to Reproduce

1. Set a DST-affected time zone
   Set your user profile and/or calendar time zone to a DST-affected zone, for example Europe/Rome.
2. Create an event that will fail on save
   Open the Team Calendar (space or personal), for example:
   https://risbz.atlassian.net/wiki/spaces/RII/calendars

• Create a new event with:
  • Date: 29 March 2026
  • Start time: 12:00 AM
  • End time: 2:00 AM
  • Click Save.

• Edit an event into a failing state
  • Create an event that does save successfully with:
  • Date: 29 March 2026
  • Start time: 12:00 AM
  • End time: 3:00 AM

• Save it, then open it in edit mode.
• Change only the end time from 3:00 AM to 2:00 AM and click Save.

Expected Results

• The event is created or updated successfully and appears on the calendar; OR
• If 2:00 AM on the DST transition date is an invalid/non‑existent local time, the UI:
• Prevents selecting that time; or
• Shows a clear validation error explaining that the selected time is not valid due to a DST change.

Actual Results

• After clicking “Save”, the button shows a spinner briefly (~1 second).
• The dialog does NOT close.
• The event is NOT created/updated.
• The event does not appear on the calendar even after reloading the page.
• No error or validation message is displayed to the user.

Workaround

When this happens, the issue is caused by Daylight Saving Time: the calendar is rejecting times that fall into a “missing” local hour (for example, around 2:00 AM on the DST change date). As a workaround, please avoid using that specific time. You can instead create the event with a valid range such as 12:00 AM–3:00 AM, or adjust the end time to 1:30 AM or 3:00 AM. In our testing, these ranges save correctly. If you must represent 12:00–2:00 AM, you can save 12:00–3:00 AM and clarify the exact window in the description.