I'd regard 50-70 minutes as the right range for good minutes. Some research was done a while ago (not by me) which suggested the sweet spot is 60 minutes and as close to that as possible is best. If you keep that up consistently you should get proficient game shape more often than not.
The most difficult thing I find is getting away from game shape being 7 at the start of the season. If your players are mostly strong now you're on the way. Mine for instance are mostly still respectable. Once your players are at 9 its my belief its easier to keep it there than it is to actually get there.