Personally I would leave them until they get more roots to dig them. The bigger they are the more they can take. I believe they need the cold to make them strong.

If they are 12" tall they should have enough root to transplant. As for me I would take about half and transplant and leave the rest and wait and see which survive if not all.
Then the next time you will know which is the best system to use later. For me the fun is in learning what works in my area and it is an ongoing event.
Paul

Are they hardy hibiscus or rose of sharon seedlings?