I hate to sound like a lawyer, but it depends.
It depends on the weathering
It depends on the running gear of the tank (rubber road wheels or not?)
I built a Churchill several years ago. The best way to do the tracks was to put them on early in construction and then paint and weather the tank when completely built. It really was the best way, and it turned out pretty good if I do say so myself.
To try to put the tracks on after the tank was competely built and painted would have been much more difficult.