While I've seen a lot of discussions on the pros and cons of Autopilot "hold steering wheel" prompts and Elon's tweets/blog posts about the timing, I haven't seen anyone do an organized look at how often they occurs or what factors affect them. Today I ended up going on a wild goose chase to central NJ in basically ideal conditions (mild traffic, light wind, well lit but overcast, big well marked lanes with slow curves,) so I decided to use my Apple Watch stopwatch to measure the timing. At both 60 and 65 on freeways I saw a very consistent 2:05 between prompts - unless there was a car in my lane being followed (in white on the dash) around that time, in which case it extended out to 3 minutes even if the car wasn't there for most of the three minutes. Using the turn signals to change lanes appears to reset the time interval, as long as it occurs before the prompt appears. After the prompt appears, it will not clear the prompt or reset timing. The Commodore Barry bridge was very interesting and I don't entirely understand what I saw. The bridge was under construction, with one lane closed by cones and a reduced speed limit. At 40 mph, I got hit with half a dozen 18 second interval prompts in a row when there were no cars in sight ahead of me, even though the car was steering perfectly and didn't seem to have any problems with knowing where the lane was (you can feel/see it move the wheel more when it isn't quite sure, and of course the dash displays change.) Then it started seeing cars in front of me in the other lane and eventually in my own lane - and it ran the remaining two minutes on the bridge without another prompt. I don't quite understand it, but it seems like some combination of the Ultrasonics seeing all the cones and the radar seeing all the stationary bridge structure tripped the very short prompts - until AP saw the other cars going through without problems.