You should be reading all of the time. The common trait all successful individuals have is a thirst for knowledge.
If you don't have that thirst, you should probably not try to start your own company.
The right question here really is to ask what you should be reading. Once you figure that out, you can plan how much time you want to spend on it given all of your other responsibilities as a startup CEO.
These days, it is very easy to spend an entire day reading interesting things without getting anything useful done! :-)
P.S. - I myself am a voracious reader, but try hard to practice what I am preaching above.
