When to expect my seedlings to pop?

it all depends on how you germinated them.. if you just put them into the medium and wait (what it seems to be) then it might take a week to 10 days.. some people prefer to put them into water or a wet papertowel on a warm surface a for initial germination, and once the taproot is out, place it into the preliminary medium (rockwool, jiffies, soil, whatever) as this will let you know sooner whether germination has been successful or not.. even then after burying it into the medium it might take a few days again until they eventually peek out of the medium. just give it some time and be patient.. 3 days isn't too much if they're buried :)