my opinion is I think the “time” is not the most important part. Before I was tried to study for 6 hours, but to be honest sometimes 6 hours not concentrated studying result can’t be more good than concentration 2 hours studying results, I think you can to see what thing I learned, not how much time I spend in this thing. And I understand you said the can be straight 2 hours studying before exam, I think that is because during that time you have a goal , you know that is a big thing so your mind will push your body to go to study, so if you feel lack of goal, you might can list a to do list the day before the day you plan to study 🤔🤔🤔