air gets thinner with Elevation not by night or day. if you are on very high land where air is less dense projectiles should fly further, and also in hot countries.
at long range you dont need a silencer, the weapon can't be heard. my Infinity at 140 yards doing 57ft/lbs can't be heard but the 31grain whizzing through air can be heard as loud as a whip if you are about 30feet from its line of path. im always amazed by how loud that subsonic projectile is.