I have filed an FMR for this a while ago as I needed to calculate an expiration date for a cookie and so I had to turn epoch seconds into a usable timestamp within the rule engine.
I have also long wanted such an option. In fact, there are a few different opportunities with properties in the DateTime format that I'd like to see realized. I'd especially like math functions so that I can and subtract from datestamps in order to automate setting some thresholds without having to use funky work-arounds.
But alas, I know of no such properties for either of us. lol
What math functions are you looking for that aren't there?
You can do math in the criteria, but are more than capable of doing so in the events. It's a little clunky but definitly usable.