Depends on a lot of factors. If a fighter was getting ready for another fight and he gets offered a title shot, he would likely say yes to a short notice fight. If he is between camps and he doesn't think he's ready, then rushing in could be a bad call.
When you're fighting for the belt, you're fighting the guy at the top of the heap, so better be ready. Saying "I didn't have enough time" won't get you another title fight if you did a poor showing. The flip side of that is that you risk not getting another shot for a while if you pass it up, so damned if you do, damned if you don't I guess.