So, I had my original 720 replaced under warranty because it would not keep accurate time. it would drift an hour or more over the course of a month.

My replacement does the exact same thing.

Does everybody's 720 have this problem, or did I just manage to get two bad units in a row (seperated by over a year)?

It's a pretty common problem. Probably bad batch of timing crystals. Funnily enough, timing crystal problems seem to be common all across the Harmony line, save for the 1000 (which doesn't even show the time) and the One.

Thanks for the feedback...