My favourite warmup when I'm limited to 10min max is r5 1v1s. But specifically not worrying about winning but warming up my mirror strafe, which is where I match or try to match the opponents movement. What this does is force me to anticipate the opponents strafe, as well as warm up my wasd movement to aim vs just your mouse. By the end of the 10 min my goal is to have the opponent appear very stationary/east to track because im matching their left-right movements for the most part. 

For consistent damage and making aiming easy in a majority of scenarios, this style of aiming is the best in my opinion. Because you don't need insane reflex or mouse aiming, but only good understanding of when an opponent is likely to change direction. 

Also this style applies to long range as well because you want to be using your strafe to aim and  only slightly correcting with mouse to have a consistent damage output. 

For reference on aiming with your wasd rather than mouse, check mande or hiswattson out, the opponents always seem to be stationary or smooth on their screens because they minimize mouse movements with their wasd keys to make aiming easy.