I can't give exact figures but even being conscious that early in the morning seems to be some sort of amazing life hack, like you are sitting there going "I did it. I did at least that much today." There is some holistic benefit outside of the spreadsheet, in other words.
But regarding planning in general, I know I have made some astounding productivity gains with planning. The first time a planning session saved me four hours of work off of a six hour estimate, I put away my hotshot coder/designer mentality, redoubled my planning efforts and started flow charting, mind mapping, etc much more frequently. I don't plan everything out with exactitude, but let's just say that while I used to laugh at those obsolete books on flow charting, now I pore through them to see if I've missed any tips. And I use them for all kinds of things, not just coding. A design agency asked for my template a while back and I made it available on the web for libreoffice users.