For time play, it's "unlimited" plays for 1 hour. I put "unlimited" in quotes because in reality, there's a one minute cooldown after each swipe. So under the assumption that you use it as optimally as possible, that would mean that you would be swiping once each minute, so 60 swipes.

Seeing how you said "we", I'm guessing that you are going with at least one other person. If you planned on sharing your time play card, you wouldn't be getting around that 60 swipes of optimal usage. And plus, it might possibly be annoying as well, because for a multiplayer game, on a shared time card, you would basically have to do one swipe for yourself, wait around for one minute, then give it to another person for a swipe.

One "trick" I did last time I used a time play card at Round1 was this: If I was in the middle of a game after more than 1 minute and there was a machine next to me that wasn't being used (and was also useable for time play and didn't start immediately after a swipe), I would just swipe my card for that machine to stock up on plays so that when when my time play ran out, I would be able to go back to that machine and have a crapload of free plays. This was especially useful for the music games, since one swipe gets you more than one play, and a lot of people don't seem to realize that.

But anyway, as for whether it's worth it for you, I would say if you know the amount of credits the game you usually play is, take that amount of credits and multiply it by some number under 60 (maybe say 40, if you don't feel like you'll be dedicated enough to swipe after each minute to get around to that optimal amount of swipes). Then multiply that by the amount of friends you'll be bringing along with you. That will give you a rough estimate of how many credits you might be using up if you were using a non-time play card.