In my experiance, when they are done growing they automatically eat less. Even if I put food in with my adults every day, they won't eat every day. They just don't need as much fuel because they're done growing (for the most part).
I put in a bowel of mealies that's availible 24/7. I've noticed my adults eat a full meal on one day, and won't eat anything (or very little) the next day.
If you weigh your gecko on a regular basis, then you should notice them level off and slow down on the eating at about the same time. Once you see that then I think it's safe to move to feeding every other day.
If your gecko clean it's bowl every night, then it could still be growing. I would continue to feed it daily, unless it has an obvious over-eating problem.
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Official Leopard Gecko Freak
3:4:1 Leos - Gilean (HTCT), Aurora (High Yellow), Amber (LVPA), Garnet (Tang), Tigerlily (HT), and Mirage (SHT), Found (HT), Lost (LVPA) (1:0 more on the way! WOO!)
2:0 Cats - Troi and Mitsu (shhhhh...don't tell them they're neutered!)
4:0 Betas - So pretty, yet so violent!
1:0 Husband - Eric (He's a lot of work, but it's worth it.)