I realize this was asked back in '12, but did you find a solution to this? I'm also trying to work with dates in ZP.
For example, I take a date from a Fiverr gig, say 2012/5/1. I'd need to first work out how many days (or months) from gig creation to today. Then second step to set my own parameter, i.e. if gig created within last 90-days then keep. If gig is outside 90-days, then discard.
I suspect I'll need to use extra code to perform this, but thought I'd ask here first.