Relax, LGA's Terminal B and D are both part of the Central Terminal, think of it as part of the one hand with 4 fingers/short extensions - starting with A on the right, B, C and D on the left - they are best walked instead of going outside to wait and hop on the shuttle for a 15 to 30 seconds ride on late evening - maybe at best a 4 to 6 minutes walk with luggage in tow, seriously.

Compared to YVR, our LGA is relatively small and walkways are short and directions/signage are fairly good - here's a link to the terminal map - gates assigned to the airlines might not be 100% updated & D has always been AA and C for United & others.

http://airportterminalmaps.com/image...urse-map-1.gif

Typically, used for domestic arrivals & departures only, most flights would've departed by 9 PM for their last run to places like IAD, ORD, DEN, DFW or BOS, etc. and usually by 10 PM, it's incoming or arrivals from other regional airports or hubs. Arrivals & Departures are on 2nd level, including food services & club/lounges (closed by then) and ticketing, and there will be plenty of chairs & places for the rest of family to sit, relax & wait for your arrival & checking the flights on TV monitors. Luggages come out relatively quickly downstairs on level 1, and, yes for different terminals/wings on its own, you can walk it upstairs or take the elevators.

Lastly, if you stay upstairs on arrival - it's fully enclosed, air-conditoned corridors and walkways from terminal A all the way to D as you can see from the map, there's absolutely no need to walk outside into the warm/hot & humid weather like yesterday - today, much cooler but still a bit on the sticky side.

Ground maintenance & other activities will continue and it's not as if the entire airport is deserted or empty of ordinary folks, and it's patrolled by LEO's (PAPD) and TSA people still guard the entrances & exits - we've come home late at 1 AM and stumbled into the terminal, and there will still be a taxi or 2 outside (or car services since there's several of you) - and then, by 4 AM, folks start arriving for the morning departure - even before the airline counters are open for "assisted" check-in (been there at 4:20 for catching our ORD-YVR connections) You will be fine ...