Welcome to FT, I'm guessing that you are flying UA non-stop, probably on a 747-400 wide body, flying time of 12 hours 15 minutes for a distance of 5,914 miles as calculated by UA. The other carrier flying non-stop to PEK is CA (Air China) also using 747 (equipments previously flown on JFK-PEK routes since replaced by much newer 777's) Lunch is served on this route in the main cabin (economy) once it's up at its initial cruising atitutde, perhaps 1.5 hour into the flight after/with a beverage service - and shortly, thereafter, overhead lights in the cabin will be dimmed, as some pax do want to rest/sleep (ha ha, LOL - not really, but ...)

Pax sitting by the windows are asked to pull down the shades and use the individual reading light above them to read. Not knowing the time of the year you are flying, it's hard to say how many hours of outside darkness you will get over this route. It sounded like you haven't flow much - here are some suggestions to help you be a bit more comfortable en route: bring the following with you: a firm travel sized pillow for the lower back / act as seat cushion, a set of (inexpensive ones from Sony will do) noise-cancelling headphone to listen to IFE and/or your own iPod or MP3 player, and a pair of eye shades to block out cabin lights (in case your seatmate or neighbor decided to stay awake & keep the light on for the duration of the flight.)

Bonus (extra) tips: the meal portion sized served will be relatively small and UA might or might not serve a pre-arrival breakfast/snack/cold sandwich (used to but haven't been on this route in a long while and not on UA for sure) - so bring some personal/favorite snacks like crackers/chips/trail mixes/energy bar/cookies, etc. (or even instant cup-a-noodles, ask the FA to fill it with hot water) so that you will not be hungry before landing in PEK.

As for the time zone difference, you should be familiar with/learn to understand the world clock - when you flight depart out of SFO at 11 in the morning, it's late night/early morning in PEK, and when you arrive PEK at 3 PM - it's late night/predawn back in SFO. Those of us who fly often deal with this all the time with our body clock, known as jet-lag (Google it) - so you really should eat whatever lunch is served, and try to sleep for at least a few hours as it's the overnight hours already in Peking - or at least close your eyes with the help of shades & ear-plugs, until it's close to landing time. It's not going to be easy if you are just starting out to join the FT crowd but you will learn the ropes, sooner or later .... Make the best & most out of it (so glad that I no longer live out of the suitcase & carry-ons )