I usually like to wait till they are an inch or two long or longer and in multipals.
Meaning they would have to be at least three or four or more roots.
Use your judgement.
Ask yourself would these roots be able to feed the size of the cuttings in question?
Beware!
The young roots are tender so use extreme caution when removing from the bag and potting into the soil.
They can break off very easy.
I would fill some mix intot he container and water down. Let the soil settle and then place the rooted cutting into the container gently. While holding the rooting cutting with one hand you gently fill with soil on top of the roots and around. Tap the side of the container with a hard object to settle the soil and water.
Hope this helps,
Good luck