The frames have nothing to do with how long you can make a replay. In Toribash, if you change a single joint's state more than a certain number of times, then the replay won't save anymore. I don't remember the exact number, but I do know that it's a lot higher than it used to be. It used to be a somewhat common problem to run into the so-called "joint limit", not so much anymore.
As for what the longest replay actually is, I'm not sure. I do know that a certain someone is making a very long replay, which I'm very excited about seeing in the future.