Warn about silly times

[djc]

From Gerv:

Do you think perhaps the AWMY link creation form could pop up an "are you sure?" warning if the meeting is arranged for between 8pm and 6am in the timezone where the meeting is being held? That might prevent errors like the below, where a meeting was arranged for 1am when they wanted 1pm...

(Originally reported on Bitbucket as #4.)