I've flown out twice in the last couple weeks and here are my data points. I have precheck and traveled with just a carry on, but got the story from others I talked to one flight.
1. Sunday afternoon flight, got to the airport around 1. 3 checkpoints open and full lines, but not extending past normal waiting areas. Precheck was only open in one checkpoint and took about 10 mins. The guy next to me on my flight had no special access, arrived around noon, and said it took him about an hour and 15 mins to get through.
2. Tuesday afternoon flight. Arrived around 2pm. No wait for precheck and normal line only had maybe 15 people in it.
3 hours seems crazy early, but I haven't been there when they have one of their lines out the door days. If you do get there early, there are plenty of breakfast tacos to be has while you wait.