Well, I haven't seen the issue in which the Fantastic Four meet with a lost Time-Keeper, but as far as I know they have the ability to change sizes, use time manipulation, redirect nexus energies, raise shields and summon characters from different time-lines Immortus style.
They have no prep feats aside from manipulation and trickery, so I give it to team wizard in prep. They can probably overcome Merlyn and Strange in a single battle.
