It's an interesting question, still it might just have been as long as they could keep someone's Z-Space parts from floating away or something, the limit could have been a whole day or just one hour, worse it could have been like the Play Station game, 2 minutes, or worse still, like the TV show, 10 seconds (I assume Jake had only 10 seconds total in Tiger morph, no other sane thing could cuase him to run out as a tiger, scare two guys, then immediately morph back to human while still in the yeerk pool)