Understanding Driver voltage ratings

Hello, this is my first post ever to a forum of any kind and I come seeking the wisdom of the great Flashoholics. My questions are as follows: 1) If I have a drop in rated for 2.7-4.5v, will it over discharge an 18650? 2) Is it correct that the lowest safe voltage for an 18650 is 3.0v? 3) How would I calculate the runtime of a drop in on a specific battery?
I believe I posted this thread in the correct section of the forum, I apologize if I did not.

2.5v is the low voltage standard from which you do not want your lithium ion battery to go below. If you are using a "protected" 18650 battery, then it will shut off automatically for you at 2.50v. If you are using unprotected 18650 batteries, then its up to you to keep it from getting too far discharged. However, I will say that on most lights you can usually tell that its getting close to needing a recharge when your light exhibits dimming. Dimming will start happening before (above) 2.50v on most lights. You would want to test your light to know for sure.

Not sure I understood your question completely so feel free to ask any more that you would like.

Thank you hiuintahs, I had read that the lowest safe voltage was anywhere from 3.5v to 2.5v on various websites. Folks on CPF seem to know their stuff so I figured I would ask here. Thank you again for your prompt reply!