what time is the first bus from chongqing airport to Dazu and how long does it take.

Well, as I know, there are only two schedules every day. One is at 12:30, the other is at 17:00.
So you are suggested to take subway line 3 at the airport, get off at Lianglukou Station, Exit 3. Then walk south around 730 yards to arrive at CQ Bus Station.
There are several direct long-distance buses that can take you to the destination. They depart at 07:20, 08:00, 08:20, 09:20, 10:00, 10:30, 11:40, 12:00, 13:50, 14:00, 14:50, 16:00, 16:30, 18:00 and 18:20. The duration is about 2.5 hours.
You need to catch the early bus. Then you will have enough time to tour around.