If you open the vents too early, you could dry out some that are still in the shell, making it hard for them to fully hatch. Better for the 1st ones to stay damp for a few hours, in my opinion.
Congrats and good luck. If you have a forced fan incubator you do not need to open the vents at all unless you see water droplets on the window. Otherwise, I'd leave them be until the hatch is complete.