Wow that is some long roto! Are you serious that your rotoing shots 3-5 minutes. My first suggestion, get out of that workplace unless you really want to be there. All joking aside here are some tips.
1. Look at the natural motion of the clip. Ram pre-view and see where the camera motion or motion of the talent stops, and goes in a different direction. Place keyframes there first.
2. Use multiple mask for things such as one for the forearm, another for the bicept, another for the shoulder, ect.
3. Here is the best tip I can give. Track the shot first. Then attach a white solid to the track. You now have the motion of the clip. Put your masks on the white solid. Lower the opacity down to 50% and you will be able to see your masks over the footage. Next use the solid as a luma matte to roto the footage. You can feather the edge in the edge feather section.
Hope these help.