do it until they have roots coming out. you'll want to make sure to let them breathe though, a couple times a day at least since those containers are so small. i'm not sure how fast they'll use up the available co2 in there, but giving them fresh air a few times a day won't hurt them. i just got my first clone planted in my hydro system =] i used a tray though. you might want to invest in one of these, it was like $5.