For years, I was living really dynamic life and went to sleep really late and it all worked fine.
My routine was: breakfast, faculty, job, second job, TV, sleep.
In that mesh of different activities, I never felt the burden of the brainwork. After faculty obligations and the first job (sales representative), I was mentally fit and could work for hours. (Luckily), my second job was as a karate trainer (kids and adults). I needed to plan the training and deal with preschool kids, as well as adults. That required a lot of physical activity and creativeness which engaged my mind on a different level. Nowadays, when most of my days are just mind work, I started to have problems with sleeping. My brain is working for hours after laying in bed and I just can't stop thinking.
After countless nights of insomnia, I tried to do training, reading, writing, playing guitar between the mind work and sleep, and it worked every time! I guess that can be a good way to turn the brainstorming mode off - just physically do something else, totally unrelated to work.