I deep condition overnight about once a month. It's usually a combination of time constraints and wanting to pamper my hair. I apply the DC, put a cap on, and tie my scarf over it. In the morning I rinse the DC, and my hair is butter soft.
I just started baggying overnight on my whole head this month. I apply a moisturizing leave-in or my moisture mix and I follow with oil. Then I put a baggy on and tie my scarf over it. In the morning, my hair is super soft and moisturized. I love the results of doing this, and I'm wondering why I never thought to do this sooner.
I agree with MsDee regarding overconditioning. I think the frequency and type of product are what result in overconditioning, not the length of time unless you're dealing with ApHOGEE or some other time-sensitive protein, etc.