Its not that simple. Well, it usually isnt that simple. There are a lot of factors here.
Just because a male mounted her, does not mean she is inseminated. Just because she is a certain size does not mean she's ready to breed, produce eggs or lay eggs. Sometimes you sit around twiddling your thumbs for years waiting for IT to happen, even thought they are the "right" size and he's mounting her daily.
The number I have heard is around 30 days from insemination to laying. I have no way to verify this as mine "breed" almost daily and lay regularly. They do not lay eggs in their burrow. You will see her up and around and pacing at hours where she normally doesn't, and hanging out in areas of the enclosure where she usually doesn't hang out, and she will likely dig several test holes before actually laying. Many females will drop a few dud eggs above ground, just out in the open, before they are ready to procuce the real ones. I describe it as sort of priming the pump. Also, fertility is often low in their first clutch.
All of what I am saying is generalities and likelihoods. Some lay a 100% fertile clutch right after the first time they are bred, even though they are still under size according to the experts. Some never lay at all, even though everything seems "right". Just be patient and realize you may be trying to get this done for a long time before it happens. Tortoise breeding is a patient man's game.