Scheduled publish time changes to default of 12:00 when using slow computer

Description

Steps to reproduce

1. Open an Alloy sample site.
2. Click F12 and open the Performance tab.
3. Capture the settings.
4. Set 6*slowdown to CPU.
5. Go to edit mode.
6. Edit any page.
7. Click Schedule for publish.
8. Choose any time other than the default, 12:00.
9. Click the Schedule button.

Expected:
The chosen time is set as the scheduled publish time.

Actual:
The default, 12:00, is set as the scheduled publish time.

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