My theory (first try):
If the restaurant is across N's property, then in general a restaurant worker (or owner) would have been in N's area already and hadn't to drive up and down by night, seen on surveillance. His vehicle could have parked across N's property at the restaurant, from the worker's shift start to the time, when he would have needed it again.
Also he would have had the opportunity to stalk N's property by night, after shift end, a few times previous to the date of N's kidnapping. Again: his vehicle could have parked across the street at the restaurant, when he was scouting N's property. Again nothing interesting to be seen on surveillance, only a worker, who arrives for his shift and leaves at various times after his shift (as often usual for these people).
From Saturday to Sunday the time of restaurant opening maybe more extensive (Idk the restaurant), so it makes sense, when the attack on N started late in a weekend night.
A restaurant worker would probably know Nancy and her large property, maybe also knows of her Celebrity daughter. To get ransom could have been an idea, which developed more or less slowly. Debt, addiction to alcohol and/or drugs - who knows, how necessary it seemed to get money.
All MOO and speculation.