I was actually able to run data for April - October for all tv and then regional sports networks. I looked at M-F by hour for 6p-12a. TV ratings are the percentage of the population viewing in an average minute.
For all of TV, viewing is highest from 8-10. Big drop off in the 11-12 hour. 6-7 is highet
Total TV
6-7: 18.1 rtg
7-8: 20.5
8-9: 22.5
9-10: 23.0
10-11: 20.5
11-12: 15.6
for the average regional sports net, 9-10 was the peak with 8-9 and 10-12 right behind. 7-8 and 11-12 have the same average, quite a bit higher than 6-7. Of course, a lot of this is driven by programming, not many games start before 7 and prime time programming concludes at 11. So a little chicken and egg.
RSN
6-7: 0.13
7-8: 0.38
8-9: 0.61
9-10: 0.68
10-11: 0.61
11-12: 0.38
Ultimately, I think this shows you want games over by 11 if possible- 11 seems to be that time when a lot of people go to bed. I think that suggest a likely start time between 715-730, which is kind of where we already are, no?