my groups typically use about 20-25 hours for a game , I think.
we have a solution where the game is on cardboard, and we can store it in an archive drawer, without packing/unpacking each time.
we typically use 3-4 6 hours sessions, we calculate most things, and to speed it up, the inactive side can be in charge of plotting numbers into a battlesim. The longest moves are usually italy, and USA/UK. italy takes the longest because we at this point plan the entire italy/GER/jap turn, gotta figure out if italy will canopen or not, and where it can put its fleet.
US/UK takes long time because it is the first ones to combatmove after the main axis have moved. caluculating fleetbattles takes long.