Dale, what size is the dot? 1MOA, 2MOA, . . . ?
Even a 1MOA dot at 400 yards is a 4" circle.
A magnified crosshair type optic with a red dot on top of it for near and far, is probably your best "fast fix". And given your time constraints that may be the best solution. It doesn't have to be a night force and an aimpoint, Walmart will do just fine.
With that said . . .
The best way is to learn to use your iron sights as they were intended. But to do that well takes time. Plenty of time. . . . and consistent ammo.