NATIONAL rental desk at Milwaukee International AirportMilwaukee International Airport is open at the following times: , Monday from 00:00 until 23:59, Tuesday from 00:00 until 23:59, Wednesday from 00:00 until 23:59, Thursday from 00:00 until 23:59, Friday from 00:00 until 23:59, Saturday from 00:00 until 23:59, Sunday from 00:00 until 23:59