A pre-sprouting seed question

I have heard many of you rave about pre-sprouting seeds, i.e. on damp paper, so you don't commit to compost until you know they are viable seeds...

I've done it for the first time, and now have signs of sprouting on my seeds. cosmos, mangetout peas, lettuce, pepper, etc.

My question is -
When do you move to soil? Using tweezers or something similar, to avoid damaging, I assume?