There are a total of 47 heats in the High School Girls' 4x400-meter relay. They started at around 1:30 p.m. and the earliest they'll end is the scheduled 5:25 p.m. start of the College Women's Distance Medley Relay. That's a lot of handoffs.
(No, I don't know how many exactly.)
The later heats involve Philly-area schools, and as always the final two are the Catholic League and Public League. I'll be back with results from those races when they come up.