I can understand about not wanting to take time off from work to get the filling fixed. Not only is taking time off sometimes a pain to ask for (depending on your job), but you also may lose income that is needed. I suggest looking for a dentist that has either weekend hours or after hours.
I would not suggest waiting. he may get lucky and nothing happens. However, he also runs the risk that many have pointed out already. If that happens he may not only lose time off from work to fix a bigger problem but it will then cost more to fix then a simple filling.