How long does it take for lice eggs to develop?

Lice. These nits, or lice eggs, hatch in about 7 to 12 days. Baby lice or nymphs are about the size of a pinhead when they hatch, and quickly mature into adult lice in about a 9 to 12 days.
6-9 days. Newly hatched lice reach sexual maturity in 10 days & can begin laying eggs.These eggs will hatch in 6-9 days & start the cycle over again.