I think there is a nag. Just spend 30 minutes testing this.
Interstate road, 12-lanes divided (6 each direction), every 3 minutes for 12 minutes (i.e. 4 times) then I got off. Exactly at the 3minute mark.
Local road, 6 lanes (3 each direction, grass divider, though the car thought it was an undivided highway and restricted AP), every 1minute for 4 minutes (i.e. 4 times).
Then I held the wheel for about 5minutes, and still on the local road it let me drive for 2 minutes, then nagged, and then back down to 1 minute. I think it might be giving me leeway if it sees me holding the wheel.