This looks like a nice addon with good potential. Certainly I struggle with people taking 5 minutes to release, get repairs if need be and get back to the current encounter. I really like the idea of automatic wipe detections as invariably I would forget to start the timer. Half the time I don't even remember to switch to master loot!
I have a suggestion - I would prefer to not automatically announce in chat the downtime duration (although certainly the option should be available). Instead, I would like to keep a history of say the last 5 out of combat times, so that if I find we are having excessively long downtimes I could click a button to link these recent times and show the raid the poor performance.
I found another addon that does something similar although I don't know if it works currently, and I don't think it does the automatic wipe detection which for me would be 100% the most valuable feature. You may be able to pull some ideas from there.
DownTimer : WoWInterface Downloads : Ace: Combat