The best solution for editing Text Presests is to start by selecting the layer and hitting the "U" key to expose keyframes. Then you can just adjust the keyframes to adjust the timing.
For even more control, select the layer and then hit the U key twice (in quick succession) to expose any property that has been adjusted from it's default setting. this gives you an idea of which properties were adjusted to achieve the effect. Try Brainstorm tool on the selected properties to randomise them and see what they currently add to the mix.
Hope this helps!
Angie Taylor animation & illustration for television, film, web and devices