Short answer is don't. I agree with Kirk.
Longer answer:
If it is valuable, rare or desired, your call on when to help. I have helped late hatchers that appeared to be shrink wrapped because I was taking the early hatchers out of the incubator. Success will be mixed, so determine how much help, care and nurturing you are willing to invest before you take action. Be prepared to cull. Do try to determine why they are not able to hatch on their own. Fix this if it is an issue with the system.
I do wait 48 hours after the first hatch. The visible membrane will appear white and rubbery in a shrink wrap. Then I will only pull the cap off and give it 12 hours to get out on it's own.
This is a learning experience and I always encourage people to learn.