I ran into this conundrum while trying to suppress active CPU alarms during our weekly antivirus scans. I don't want to discard CPU activity alarms altogether, and Outlook only has a canned rule for acting on emails received on certain days.
What you need to do is create the rule with the criteria looking at certain text IN THE EMAIL HEADER!
As far as the specific text to look for, I opted to use "2013 23:" (the clock for headers is the 24 hour variety). I left the year in there so that the rule wouldn't falsely trigger on other instances of "23:", which is a pretty generic search term.
Sure, I'll have to edit the rule next year, but this will get me by.