"plumbing"? "installation"?

It's connecting two screw fittings, and then installing toilet seat (two bolts + nuts). If it's a particularly fancy model you may have to plug it in.

This is about as complicated as replacing a furnace air filter, and takes about as long. If you get someone to do it for you, you're paying for them to drive to your house, not the actual time installing it (which is trivial).