i've opened up a number if sites (maybe 10) and rotate almost all of them into my schedule, no matter if i'm doing 2x a wk or ED injects. i try to use each site no more than 1 time per wk. sometimes it takes longer for a site to recover and if it doesnt feel ok, i will hold off on using a sore site, even if it's been a wk. over time, you can build scar tissue up in a site, even when used once a week. the dead tissue can cause poor blood flow and can make it hard for oil, hormone and waste to be broken down and carried away. deep tissue massage will help to break this tissue down and keep the muscle heathy. of course, the more oil you push into a site, the longer it may take to break down. some of the new solvents, like the ones in geneza gear, make the oil very thin and it tends to break down faster than the more tradtional oils, in my experience. still, i try to stick with my plan of using a site no more than once a wk. the needle alone can cause enough scar tissue to cause problems. if you ever find that its become harder to push a needle into a muscle, if you hear/feel "pops" and "crunches" as you push the pin in, if the oil has become almost impossible to inject, you have probably developed scar tissue and need to rest the site and ideally get some deep massage.
for someone doing 3x injects a wk, assuming you're using no more than 1-2cc each time, i would use 6 sites. quads, delts and glutes are all easy to hit. i would put no more than 3cc in a glute, 2cc in a quad and 1.5cc in a delt