Aquaponics and Hydroponics average 3-4x the growth rate and grow 24/7 (though you do need to provide lightless hours for proper fruiting). It's 100% viable and there are commercial operations right now.
I don't think you understand how much land you need to feed 1,2,4+ million people every single day. Even at 3-4x the growth rate you wouldn't fit anywhere close to what's needed inside a city.