You can see ovulation whenever the gecko starts to ovulate. Once she's developing eggs (and this is based on my observation of my fat tail gecko who has been laying regularly), you can probably see eggs pretty well about a week before they're laid. I have a lot of leopard geckos who are clearly ovulating and have mated but it's not clear whether I can see eggs, though I think, based on previous years, that once they lay the first clutch, it will be easier to see the eggs for later clutches.