@LukeOscar. Sealing takes about 20 minutes, scraping and cleaning takes about 5-6 hours... I did a 150 recently, with a heavily but poorly siliconed bottom (think 6 tubes of improper sealing)
my girlfriend and I didn't really have the right tools - get a razor/paint scraper with some new blades at home depot for a few bucks, pays for itself. I was using a chisel and she was using a small exacto in a pen style holder, it took me 6 hrs, with her helping for 2-3 of them.
It's much easier (IMO) to turn the tank on its side (even if it's very heavy). my tank was an oldschool 150 with 5/8+ glass, weighed over 400 lbs. if you try scraping it while it's upright, you're just going to give yourself a headache.