When I do S&H rotations, I aim to do each upper body part twice each week. It's a question of preference. When last I did this, it was part of a 6-7 week rotation of S&H and I saw miraculous stregth gains and lean muscle tissue gains.
However, I then didn't do any weight training for the whole of last year and just started back up this September. I have not been able to strength train more than once per week due to busy schedule, and I have to tell you that the once per week approach is working great for me. My efforts were spotty to begin with because I had visitors to stay for half of September, but once I got going in a concentrated way, I have seen great gains in a relatively short time.
What I am doing at the moment is a mix of S&H and GS. I know both sets of workouts so well, I can combine them to suit my body's needs. I do S&H purely for chest, biceps, and then a mix of slow-mo count and a faster GS count for all other upper body muscles. I am already nearly back where I was when I stopped lifting a year ago on chest, back, shoulders and biceps. Triceps are my weakest area anyway, so I don't use them much as a measurement of progress and success.
Chest and shoulders are the two muscles I have been working strictly once a week because there is too much overlap between them to make it possible for me to use a slow approach and work each one twice. And yet, these are the two muscle groups I have seen the most sustained strength increases in.
Does that answer your question?
I have always thought that weight training the lower body once per week is enough, especially if you do a lot of cardio. When I can't get the cardio in that I wish, that is when I step up and increase the lower body weight workouts to 2 or 3 depending, but this is not because I wish to speed up muscle gain in the lower body but because I need to move and sweat and burn off some calories.
Remember however that as with all facets of exercise you have to do some trial and error experimentation to find out what works best for your body and timetable.
Clare