I have never been, but I know 2 people that have been harassed about their speed in the park.
Spring time is always busy. I've been twice in late Sept. temp cool at nite 92 in the day. If all you do is ride the park, that can be done in a day but there is so much more to see and do while there.As said, watch your speed in the park. I'm looking at Oct. There are plenty of places to stay in Study Butte/ Terlingua . Riding the border road from Del Rio ro Marathon is more sceneic than I-10 . Crossing the Border to Boquillas is cool. The river road to Presideo is a must. Fort Davis , I'm ready to go back.