how long does it take for a egg of headlice to hatch once it falls off the head?

Answer 1

A lice egg is commonly called a nit. Lice attach their eggs to their host's hair with specialized saliva which results in a bond that is very difficult to separate without specialized products.

Humans are unique in they host three different kinds of lice: head lice, body lice (which live mainly in clothing), and pubic lice. The DNA differences between head lice and body lice provides corroborating evidence that humans started wearing clothes approximately 72,000 years ago

Recent DNA evidence suggests that pubic lice spread to the ancestors of humans approximately 3.3 million years ago from the ancestors of gorillas by sharing the same bed or other communal areas with them, and are more closely related to lice endemic to gorillas than to other lice species infesting humans

It takes more than a week to hatch and few day to weeks to be a grown up. SO ACT FAST OR ELSE LICE PROBLEMS ARE MORE.

Answer 2

IT seems its three days if I remember, i think thats why you treat once and then again a few days later.

Just google it.