The time it takes for eyelashes to grow back is at least 6 weeks.
As long as the eyelash hair follicles of your eyelashes are healthy and intact, eyelashes grow back within 6 weeks but if your eyelash follicles are not as healthy or intact it can take 8 to 12 weeks for the eyelashes to grow back.
But for most people they have their eyelashes grown back fully after 6 weeks.
If you've plucked your eyelashes you should see the eyelashes begin to grow back within a few weeks and after 6 weeks the eyelashes should be fully grown back.
If not then something is not right with your eyelash follicles.