Four hours of DM a day would certainly help your aim, but I can imagine you'd burn out of that regimen fairly quickly. If you're really worried about your DMing abilities, just DM/MGE/whatever an hour before your matches/ scrims. You're in iron, where it's expected for people to be learning the ropes of competitive.
But DM isn't really the most important thing. The important thing will come with time and research, and that is gamesense. Especially in lower divs. I played all class backup in steel forever ago, and was absolute garbage at aiming. I still carried my own weight because I only picked fights I knew I could win.