i think that the general rule of thumb is if the clone can handle being out of the humidity dome and is able to uptake its nutrients and water through the roots then its ready to grow!
the best scenario would be to put them under fluoro's to veg a lil bit before throwing them under HID lights.
just be careful. plants that small are susceptible to drying out easily under HID's
good luck bro. if in doubt another day usually won't kill it