If flight leaves Milwaukee airport at 7:40pm, what time should I be at the airport?

Depends on where you're coming from 94 North between Illinois and Wisconsin has Construction and will delay your Drive-In. Also since it's Friday night I would make sure you're there no later than 5:30. It may also depend on if your flight is crowded

I would also give yourself the full 2 hours ahead of the flight also my friend is a pilot and there is so much to do before your flight

Your airline normaly says minimum 2 hrs bfr the FLT departs to be at the check in desk. Some days this enough and others it's not