There is, but I don't remember how. I haven't used Live Type in over a year. While I know I'm not real helpful here, I'm just confirming it's possible.
I take it that you're talking about modifying one of the stock animation samples that ship with LiveType. In which case, the only way of speeding up the animation without shortening the duration is to loop it (5th parameter down in the "Timing" tab of the Inspector palette).