On an existing event, if I edit the event, when I try ot adjust the timelines for invite and reminder, when I click on the “send invites when” button, nothing happens and all I can see is a non-working cancel option. This in on Chrome Version 81.0.4044.92 (Official Build) (64-bit).
Ran into this issue today. I forgot to set the Send Invite /Reminder dates and went back to try to edit them in the event. You can’t edit the the notification dates. I had to delete and create my event.
Also, I think at a minimum it should be defaulted to Send Invite: Today.