The seat belt sign is definitely on too long. Sure, we've only been in the air 45 minutes but we've been standing by the gate and boarding for much longer than that.
I do not know if the sign is on longer more recently. It seems to be more enforced now.
On my last flight, the pilot told us we'd be hitting bumpy air later in the flight. So she gave us a warning that the seat belt sign would eventually be on. She was very nice and landed the plane (an md 80) extremely well.
The weather in the United States seems to be more volatile than before. But it is possible that seat belt signs are on longer so that stressed out travelers are not in the back so much just hanging out.