Don't worry, lol, I did the exactly the same thing. In fact, I accidentally did it again yesterday. What's really odd is that they'll have their eye on one fly while a couple more flies are perched right on them.
Will gray tree frogs eat in the morning? or will they only eat at night?
Lilke JWells said, mostly at night, but when they're young like this you want to make sure there's always a snack available. My little guys will usually pop out a couple times during the day for a pick me up. Good idea to dust them every other feeding or so. That also has the added bonus of making it harder for them to escape before they get in the viv
How do you keep them in the viv with out escaping?
Noseeum mesh, tight fitting lids, and silicone around the doors, if you have them. And yep, there's still escapees. The first time I tried to culture them, I think more ended up in the house than the culture cup.