I bet they could check traffic flow based on the cameras, they could see if it was jammed up at that time (I agree the Merritt can get jammed up about there at sometimes seemingly random times, irritating to no end when late to the airport, etc!)
IMO, the biggest thing I think could account for the time gap in sightings between Lapham/Waveny and the NC cam in the Merritt, is that FD would have had to do some cleanup of the Suburban after he took the body out. There was blood in the garage, there was blood in the red truck, so how could there not be blood in the Suburban, plus the warrant states they found blood in exterior and interior of her Suburban. After FD took out the body to put in the red truck and before he departed, he likely had to do some cleanup on her car. Knowing that he disposed of what they suspect is the mat from the Suburban, he clearly was concerned about not leaving evidence in the Suburban. I bet he tried to look it over carefully and get rid of blood, and that might have taken some time.
Then, he would have had to make sure there wasn’t anything obvious in the red truck in the case he got pulled over, so he’d have to arrange it carefully in the red truck and cover up the body etc.
Also, while a body transfer and cleaning could be done quickly, he’d need to be careful and watch out for oncoming cars and anyone else who could spot him, so that could have taken a little time too, he probably didn’t want to be seen.
Also, if Lapham was the last place JDs phone pinged, FD perhaps spent a little time hiding her phone in the woods there. (Also what about JD’s purse/wallet?) This is a more remote part of Waveny and I recall LE brought electronics trained dogs in so LE may have thought her phone was there. I would think that FD would want to be sure to get rid of JDs phone, even if turned off, before he left to Farmington, and near Waveny, to go along with the abandoned car/abduction coverup (also her ID/wallet). Even FD would not be so stupid to take JDs phone even if turned off, (or ID) on the trip back north with him (or would he). This might explain FDs newly discovered love for spending time exercising at Waveny as some of you have reported. (I for one will not be running at Waveny again until he is in jail, and be careful at Norwalk HD too. Thank you for the heads up on the FD sightings). When seen at Waveny he might be checking out the site where he put the phone to see if it has been disturbed, etc.
If FD went somewhere else in the red truck after the body exchange at Lapham and before getting on the Merritt, it had to have been very close by (or south of that exit) because of the proximity of Lapham to that exit on the highway, as another person pointed out. Otherwise he would have missed the NC webcam on the Merritt.
MOO.