You should not hold the frogs until next spring before releasing them.
The longer you hold them the more difficult it will be for them to successfully adapt.
Especially , foraging for their own food in the wild vs it appearing in the grow-out enclosure.
They are growing and adapting to an artificial environment.
This should be done as soon as they are eating on their own.
Ideally, it should be to the -----> area they were found.
If this is not possible it should be in an area you are positive there are grays .
You will want to get them back out there asap as they will need to begin to prepare for their hibernation.