I'm guessing that one day that USF is closing at 6:00pm (on Feb 21st) is due to some kind of private event starting after that. All other days looks to be either 7:00 at IOA or 8:00 at USF (and later on the weekends).
As the other poster noted, this is a slower time in the year. For instance, looking at the Crowd level and wait time last year for the same period (I looked at the Thursday after Presidents Day as an example), Universal's crowd level was ~4 with wait times for the most popular attractions being ~30 minutes or less, whereas looking at MK the Crowd level was a 6-7 with the waits for the most popular attractions being well over 60 minutes (with some going over 100 minutes).
So in the end you'd probably be getting much more done at Universal with shorter park hours than at Disney with longer park hours.