The amount of high schools participating makes it virtually impossible to have trials of all three relays on the same day if there are other events on the oval. If you stretch Thursday, they just squeeze it in but the result is basically the longest single day of the track and field in the world. Thus the gender that gets to compete on Saturday (meet management appears to be alternating?) has to run trials in the AM and finals in the PM, with 4x100 and 4x800 trials on Friday. The big disadvantage is for the local schools as they run later in the morning and have a shorter recovery. In the past some top local schools have asked to run earlier in the morning.
I'm not entirely well versed on the specifics but I think New York public school rules state you can't go to a meet for longer than two days, which is why there is no gender overlap except for a few events that don't involve New York HS.
It is quite the spectacle and you should come and watch next year.
Dwight Ruff of Camden HS waaay back in the day (2001? 2002?) did the trifecta of winning the HS 400 hurdles at 9 AM, then running two 47-48 legs for Camden (NJ) HS when they won the HS 4x400.
In 1983, four teams in the Philadelphia Public League were 3:18 or better at noon, and West Philadelphia came back four hours later to win the whole thing in 3:12-3:13 (don't have the program in front of me right now). That's actually one of the saddest parts of the meet; the City of Philadelphia used to have very good track teams but now there are so many charters and magnets and whatever the teams just aren't very deep. The Catholic League is much more consistent nowadays.
Could some explain the reasoning for running the high school mile relay trials and finals on the same day?
You never ran more than one race in one day at a meet!??
Sure but I never hit crazy times in more than one event on the same day. Its fine for 100 or 200m runners but anything longer, and for most athletes, you're not getting 2 notable performances in the same day. You could have 2 good performances, sure but you should not be asked for 2 "Penn relays winning" 4x400 performances in a six hour period.