It all depends on rust. Are you going to torch off the U-bolts or are you going to unbolt them? If they are rusty, it's going to take awhile. Are the front spring mount studs rusty? If so, you're probably going to break a stud or two.(or all of them) Are you putting new front hangers on the new springs or reusing the original hangers? If the main eye bolt is rusted inside the spring bushing, it's going to be a PITA. Not trying to scare you but there are a lot of unknowns which makes it hard to estimate a time.