When you move a repeating event on an iCloud calendar, both the original and new times will block off time on your scheduling page.
For example, if you move a repeating meeting with a 9 a.m. start time to 9:30 a.m., both times will show as unavailable on your scheduling page.
Delete the repeating event that you moved, and create a new event for the new time instead. This will free up the original time.
If deleting the event does not work, try deleting the very first event in the repeating sequence. If neither options free up time, you may need to delete all repeating events in the sequence.