Ask yourself this simple question: Would you rather spend two hours sort-of-studying-while-sort-of-goofing-off, or just 20 minutes studying intensely (and remembering much better) and then 100 minutes goofing off wholeheartedly?
However, this momentum will always have both an upward and a downward curve. After a while the momentum will begin to run out, after which point it is a good idea to change activities.