Hi Marek,
we usually group house the mice directly after implanting them with the Grinlens implant (and try to implant the animals from the same cage as close together as possible). However, we also implant the grinlens directly with the baseplate, so it is protected.
That being said, I doubt that the mice will damage the implants even if you implant only the grinlens first and cover it with something, so i think you can definitely group house them as soon as possible!
Cheers,
Florian