Time spent on each lesson

I am really enjoying your guitar theory book. I have been playing for many years and your book is really helping to fill in the missing pieces. My question is, how long should a person reasonably spend on each lesson before moving on? For example I am studying the intervals and it appears that i should memorize the locations on the neck before moving on. I know everyone learns differently, but just an on average how much time should i spend on it? Maybe I can just work it into a daily routine and keep moving through the book.