Around 2 hours 12 minutes to beat, not including the 1 hour spent beating Easy mode. The game forces you to beat Easy mode first, which is only 4 stages, then Normal, which is 7 stages. Hard mode has some additional stages too. While beating Easy mode I had upgrades that carried over, but I am only including the extra time spent to beat Normal in my completion time. I also didn't include the 9 or so crashes of the game on the emulator in my completion time of either difficulty. That probably added over 30 minutes since I had to reboot the game each time. This version has the crashes edited out but everything else is shown. I posted the Easy mode playthrough up separately here:
• After Wave : Downfall (Switch) Unedit...
Neither one of these are straight through playthroughs since there is a lot of levelling up, replaying stages to get more upgrades. The game crashes during the loading screens between stages, when it crashes, so the auto save kicks in and no progress is lost.