Just sent this reply to birder who asked for my advice regarding best two weeks to visit Beidaihe (in autumn):
During the year, best two weeks for species diversity is in May, around 4-18: hence several tours at this time (I helped start Sunbirder tours)
Autumn is more protracted; but as you've seen in report, can be some impressive movements of raptors, cranes etc - mostly way bigger than spring, and can get falls and so forth.
For autumn two weeks, I think October, maybe around second and third weeks: still decent diversity, with some chance of late birds such as cranes.
When migration is slack [between cold fronts; helps to have better weather forecasts now, inc over internet], great if have a vehicle so can explore nearby places. Report mentions Qilihai - Seven Mile Sea, where there's decent chance of waterbirds, say. Well worth a night or two on Happy Island.
In May last year, I went to Heavenly Horse Lake, or Pegasus Lake, maybe a couple of hours by road west of Beidaihe. Thought it a tremendous place; it was May, and only partial coverage but lots of Wood Sandpipers n so on, with Amur Falcons hovering over the grassy areas. This place deserves a whole lot more coverage; but I'm yet to see more records - was taken by a Beidaihe guy who likes taking bird shots, told us of seeing whooper swans etc there.
Old Peak not so good in autumn, though I enjoyed a Nov day, which included several Pallas' Rosefinches.
November can be fantastic, too. BUT low diversity; can be tough to see big "wave" of cranes etc - yet if you do, one of most memorable birding experiences you can have anywhere I believe. Some birdforum threads including posts on Nov sightings by rockfowl, aka Mark Andrews of Wildwings: he tried November once after I waxed lyrical about the cranes, Oriental storks and other birds at this time. He has been several times since.
Timing harder now I think, as warming has tended to make crane waves later. But even some years ago, I co-led an Ornitholidays tour with cranes as focus; thought I had dates right, yet we didn't get big wave, just managed five species. [I remember as arrived at hotel in Beidaihe; participants putting bags into rooms, I scanned sky before going indoors, saw red-crowned cranes moving over, and ran indoors yelling - folk stopped unpacking and came out to see the cranes just disappearing to south]
- might be worth putting November into "maybe" pile, should you and friends enjoy a first trip. Get variety of species out of the way, then see about the spectacle, and megaticks.
Also, Beijing worth a day or two. There's site to north for ibisbill, crested kingfisher, long-billed plover. This is at a river. Also Wild Duck Lake gets good birds, tho I've only made quick stop seeing little: maybe bit like Pegasus Lake.