Let's be careful about how we define our system. Are you "shooting" the rubber band horizontally relative to the ground? If so, then air resistance will decrease the horizontal distance the rubber band could travel as opposed to in a vacuum, while all other things are equal (such as the angle you shot it at, how much you stretched the rubber band to shoot it, etc.)

Air resistance or "drag" will slow the rubber band down in the horizontal direction. Since velocity is distance/time, slowing the rubber band down means less distance is traveled in a shorter amount of time, or it takes longer for the rubber band to travel the same distance than if it were moving faster. I hope this helps!

Air resistance slows things down, and the faster something travels through air, the greater the resistance! When you launch a rubber band, it initially travels quickly, but it slows down after a few meters due to air resistance. If there was no air resistance, a rubber band would fly a lot further!