I think its whatever you are comfortable with. Working out is enjoyable to me so I have no problems getting something in whever I am in the mood for it.
Yesterday I went to the gym before work and did a quick run on the treadmill and a spin class and then in the evening I had dragonboat training which consisted of 20 minutes strength/condition work and about 75 minutes on the water hard paddling.
I tend to do mulitple sessions more frequently in the warmer/lighter months as well...it's just inspiring to be out and about moving