1. Avail of the first flight that works you
2. Let your friend fend for himself
3. Meet your friend in Shanghai
4. The Hilton idea doesn't work wrt T2

While I'm not suggesting that hanging out in a t2 lounge is significantly inferior to doing the same at any random Starbucks, leaving should be your #1 priority.

Basically, if the 4p flight has a takeoff slot, and a seat for you, grab it! Your friend might end up hanging around t2 for 10 hours because his 7p flight doesn't leave until 3a, but there is no reason to put yourself in the same position.

Perhaps you could advise your friend to join our wechat group; collectively, we are pretty good at addressing travel related anxiety.