I switch out a lot around labor day - mostly so I can have space for my kids Fall clothing and have access to hangers. I leave just a few summer items for us to wear during Fall transition.
As of October 1st - we were 100% switch to Fall though and all summer is either put away, up on ebay or donated already.
It is quite a process for the 4 of us ladies and usually takes me about a week to complete. But I love it - just touching, hanging and smelling those new clothes. ahhhhh... I love closet transition time...