I have a comments field on the spreadsheet that I'm working on, which must be
completed if the value in another field = "N". If the value is anything
other than "N" (including blank) a comment is not mandatory. I've wandered
around the forums looking for something similar and can't find anything.

In the same spreadsheet, I also need to validate that the time is entered as
HH:MM in 24hr clock.

All help is greatly appreciated!