How to get from Shanghai Marriott city centre to pudong inernational airport?

Oh, generally speaking, you are suggested to arrive at the airport 2 hours in advance for a domestic flight and 3 hours in advance for an international one.

From your hotel, take subway line 2 at People's Square Station to the Airport Station, Exit 1 directly.
It takes around an hour on the way with the ticket fare of CNY 7 per person. So you can decide your starting time according to this duration.