Khurram,
The later you go in the season and the less warm the weather will be. So late November is nice, not cold but cool and pleasant. Havasu is at 3000 feet elevation roughly, so it doesn't get cold there. It's a little like Zion canyon, at the floor of the canyon. It's nice year round. The fall colors are not, in my estimate, the main interest of Havasu. The main interest are the falls, especially Havasu, and before you reach it Navajo Falls. You also have Mooney falls, named after a miner called Mooney, past Havasu Falls. You can do them all in a day. The best time to photograph the falls is late afternoon so you have open shade.