Sit for Long Hours

Yes, building stamina for peak concentration for four hours at a stretch is a part of the GMAT Preparation. Dont leave this for the end of your preparation; rather, try to study in long sittings. Have as many four hours sittings as possible. Further, keep taking one test per week in first two quarters of your preparation; in the third quarter, start taking two tests per week and in the last quarter, take two three tests per week.