I would only like to train GS in very unusual circumstances. I have been playing since season 10 and have never done it. However in retrospect if I had done it last season for the playoffs I may be in the ABBL right now (being slaughtered). So it is maybe worth it the week before the playoffs if you think you have a great chance to promote but need an extra edge. Normally as was said 48-75 minutes is good. My federation is doing a season long, detailed and exhaustive study of minutes and GS involving dozens of players and we have already noticed some bizarre trends in players getting crazy GS results from sensible minutes so do expect a large random factor. However if you stick religiously with 48-75 every single week the majority of your team will be in great shape every week.