A calender month as in every 30 days, or 31? (or 28??)
It's 30 days. I assume it works the same as source Merits, which means it's 30 days exactly up to the second.
Am still a little unclear about the deleted posts how they count.
You can only bump by posting if you haven't posted in the past 7 days (and it doesn't matter if that post was deleted or not).
Your bump is only valid if your post doesn't get deleted.