It looks like one must enter a time in the format 00:00 or you will be unable to save the task. The page reloads with the message "Failed to add scheduled task" and no other information about why it failed.
Just tried this out and I can confirm it. Few different things could be done here. 1. Placeholder in the input to show 00:00 2. Error handling that retain submitted values and show a hint about the validation failure 3. Do client-side validation