It takes between 1.5 to 4 hours to replace a toilet if you are hiring a professional plumber. The time depends on the type of toilet you are installing. The one-piece toilet replacement will take 1.5-2 hours, two-piece - 2-2.5. If you need a bowl replacement for a wall-mounted toilet the plumber will spend 2-3 hours. The problems with your water tank inside the wall however is a different story and will take 8-12 hours. If you are thinking of doing it yourself and don’t have much DIY experience add 1 to 2 hours to the times listed above.