The temperature should be fine to release them if you want. I found a couple of Peepers outside here today (and many other frogs) and I'm at a similar temperature as you (I'm in Ontario). You haven't had them for long, so I don't think that's a worry either. As long as they haven't come in contact with any foreign froggy diseases from other frogs you may own, I can't see a problem.

You're right that injured frogs don't typically make it in the wild, the slowest get eaten so good for you for helping the little injured dude out and you can feel good about sending them on their way if that's what you choose. I'd probably be a sucker like Don and end up keeping the formerly injured one at least (I have a 3 legged Gray treefrog that I couldn't turn down). Only keep them if you are prepared to house and care for them for life, but I'm sure you already know that.