Hello kandhi
From my experience early fall and late spring are the best time to transplant here in Santa Clara, Ca. My Michelia's growth generally slows down during the middle of November. In transplanting Michelia during the fall (60 days of 65-70+ degrees) I move the whole root ball intact to the new pot with a slow release fertilizer at the bottom, with a pencil I slowly spread the roots around the perimeter and bottom slightly trying not to break any roots before filling the pot up with new soil. Hopefully my experiences will help you decide whether to transplant or not.
Cal

Cal, It is in 70's temp now, I am afraid I might kill it by repotting. Below is my plant that looks very healthy, I hope to maintain it in that container until next spring,is rootbound not good for michelia?, below is the pic I took today

Hi Kandhi
Nice plant! Something to be aware of, a very root bound plant can prevent water from penetrating the soil or it can prevent the water from flowing out of the pot. In the first case the plant does not get enough water and in the second case too much water.
Cal

Nice plant! How about the fragrance? Can you describe or compare it?
kevin

the plant is still blooming. The fragrance is like ripe banana. The plant is indoors now and 1 bloom perfumes the whole room.

Mmm. Looks very healthy and well tended, too.