fix: appointment slots start and end time

[SebastianKrupinski]

Resolves: #6407 Resolves: #5913

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 23.43%. Comparing base (492beb5) to head (6e06e87). Report is 4 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #6499 +/- ## ============================================ - Coverage 23.46% 23.43% -0.03% Complexity 453 453 ============================================ Files 247 247 Lines 11728 11724 -4 Branches 2212 2223 +11 ============================================ - Hits 2752 2748 -4 Misses 8656 8656 Partials 320 320 ``` | [Flag](https://app.codecov.io/gh/nextcloud/calendar/pull/6499/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | Coverage Δ | | |---|---|---| | [javascript](https://app.codecov.io/gh/nextcloud/calendar/pull/6499/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | `15.03% <ø> (ø)` | | | [php](https://app.codecov.io/gh/nextcloud/calendar/pull/6499/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | `59.29% <ø> (-0.08%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

---

🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests
• JS Bundle Analysis - Avoid shipping oversized bundles

[SebastianKrupinski]

/backport to stable5.0

[SebastianKrupinski]

/backport to stable4.7