How many days to spend in Jiuzhaigou and Huanglong

Hello,

My fiancee and I are planning a trip to Sichuan and wondering how many days do we have to allocate for JZG and Huanglong, we like to walk around (not a bus hopper kind of tourist).
Is it better to take the bus in then fly out or is it better to fly in then take the bus out.
Will 3 days be enough (including 1 day for bus travel) if we fly in from Chengdu early in the morning, or fly out late at night