sounds like a pretty good system to me. my system is driven by laziness - 0 minutes for everybody. adjust at midterms for failing players if i remember, if not, just deal with it. i often go 0 for entire periods and usually you lose 1 player, sometimes 2, sometimes 0. probably like 1.2 on average. and mostly young players, which rarely matter too much.
for someone who cares, i would still go with the 0 minutes for everybody scheme, just i would always adjust as soon as midterms come out. when midterms come out, for guys in the 2.2-2.4 ish range, i would usually give 4-6 minutes, but sometimes 0, depending on if i need them, and how much i want to use those minutes elsewhere. for guys in the 1.8-2.2ish range, i usually give 6-12 minutes, depending on where they are, and the previously mentioned factors. then for guys in the 1-1.8 range, i usually go in the 10-15 range, but if i really really need a guy, i will sometimes even go with 25. very rarely. but sometimes.