usually restaurants have a Server Assistant position every night and the server who works that position gets min wage.
good servers can easily make anywhere from $15-20 an hour on tips. sidework is a part of the job description. to be honest if a server has a 3 table station in a dinner or lunch rush 3 - $5 tables an hour should be no problem a good server should have no problem getting 5 or more! even if you are a $2 tip level server with a 2 table stattion if you turn those tables 2 times an hour you make $12./ hr
the hour they work before and the hour or so after they work is so they are set up so when they are making tips they can serve as many tables as fast as possible.
usually the smart servers know how to do their sidework as the night goes along this way when their shift is finished they can leave quickly. usually the servers who complain about not making min wage during their sidework are the newer servers or ones who spend their time in the break room instead of doing running sidework.
jobs with tip based pay are written into the min wage laws. some states like California Oregon, have laws that dont include tips in those states servers get paid min wage in addition to their tips.