Good points Eric - I just went back over the last 4 years for average starter minutes (using top five players so not Doty for this past year for example even though she started some games.)
2013 - 27.4
2012 - 28.9
2011 - 30.8
2010 - 26.6
The 2011 season was an aberration because of the bench - it consisted of Dixon who average 22 minutes, Walker (freshman) who average 19 (in a total of 17 games) and then Buck and freshman Engeln and Johnson - Geno didn't have much to turn to there after the graduation of Charles, Gardler, Greene, McLaren, and Fernandes and he was already starting Stef and Bria as Freshman.
So ... in an average year there are 60+ minutes available for bench play every game - if a freshman or bench player is good enough they should be able to get 15-20 of those minutes and if they are exceptional and/or flexible in position and/or desperately needed because of previous year graduations, they can get starter minutes in the 20-30 minute range. Ideally Geno would probably prefer 70+ minutes for his bench, but he is unwilling to run garbage time garbage basketball so failing talent on the bench he'll leave more starters on the floor to keep the flow on offense and defense. A bench player with potential will learn a lot more playing with a couple of starters than they will learn freewheeling with no one knowing what they are doing.
ON Edit -
Just a comparison to the Olympic team when Geno had a really solid bench ...
Bird led minutes per game with 24.9 and there were two other starters with more than 20 minutes - DT at 24.1 and Charles with 21.3. Then there were another 5 players in the 17.4-19.8 range and two more at 14.9 and 10.3 and Fowles and Cash with 9.6 and 8.3. So if Geno has some bench talent they get their minutes.