Rescued eggs hatched/release time?

Hello everyone, any advice will be gratefully received.
I have never kept snakes before and have got some grass snake eggs and hatchlings from work. A JCB was laying pipes and accidently dug them up. Some were. destroyed and the others I decided to take home and nurture.
They must have been almost ready to hatch because after two days indoors a few heads poked through the eggs. I now have 6 hatched grass snakes and four more heads poking through and a few more healthy looking eggs I expect to hatch too.
I have them in a 2ft by 18" tank with no extra heating as it's quite warm indoors. 
I have 2 inches of earth and stone from the garden with earthworms, some woodlice and some small slugs to keep them company. A small slate, flat stone & log are providing hiding places and milk bottle cap providing water.
I will be releasing them back where the eggs was found asap.
The Question is WHEN?
Some forums say not to feed them as they get by on the egg yolk for a while and to keep them until they shed then release them. Shall I release them as they hatch or wait for them all to hatch and release them together?

I asked on the RFUK forums but got mixed responses and am none the wiser.

Thanks for your advice in advance.