I think the best time to study or memorize anything is 5-6 at the morning before starting a day. Usually when I have to memorize anything I wake up at these times take a shower and start studying comapred to my other experiences this time of the day is the most efficient.
This is your routine. Someone else has the different routine which suits him better. The question is kind of odd because if the Economics is the best for studying in 5 -6 then what about other classes. Is math better at 8-9? We are all different and to the op, all of us can give just suggestions that are based on our own terms of adaptation. In the end, the op will find his own routine that suits him the best.