Removing an old tub is often the loudest day. Cast iron tubs are usually broken up in place, and the tile and backer behind them come out down to the studs. With the wall open, the remodeler and plumber can see the condition of the drain, the supply pipes, and the framing, and tell you what needs repair.
The plumber then installs the new valve and drain under a plumbing permit from Hingham's Building Department. The rough plumbing must pass inspection before the new walls go up, and in Hingham that appointment is requested by phone during the morning window, Monday through Thursday.
After inspection, the crew installs the shower base or builds a tiled pan, waterproofs the walls, and tiles. Glass doors are usually measured after tile and installed last, so the shower may be finished a little after the tile work ends.