bare minimum 1 week if you work all day everyday.
removal of glass, prep the roof, each layer of epoxy takes at least 2-3 hours to tack, and more than 8 hours to dry. application of each layer takes 30-60 minutes. need at least 4-5 thin layers. gotta let it cure for 24hours then sanding will takes 2-3 days because trust me your arms will give out fast. theres like 10 or more different stages of sanding (up to 600grit) then you clear coat, 3-4 thin layers. give it at LEAST 24 hours to dry/cure then wetsand from 600 to 2/3000 then buff, polish.
then you need to spend 7-8 hours to detail the **** out of your car inside out because by the time you're done, your car is gonna look like crap.
lol. and ^that's why im most likely not going to attempt this again. lol
IF i attempt to do this again on a friends car in the future, which looks like may happen this summer, i will take more time, and do more homework before attempting again. then pending those results, i may reconsider doing it again on my own roof. but thats stretching it. hell, i may not even help my friend just because i know how much work is involved.