With 3 weeks left, you can do ALOT, especially since you have a strategy in mind (ie. the Kaplan approach).
There are infinate methods to improve focus...I'll mention a few of them here.
It's my opinion that you can easily study 5 hours a day. Even more. It's what you're doing when youre not studying that plays as important a role. Keep the following in mind.
1. BALANCE. Since you're starting a rigorous program, make sure you keep, and stick to, a schedule that includes balance. What you eat. How much you sleep. Exercise. Fresh Air. Etc..
In your schedule, each day needs to have time identified as time for study (for studying its best to do it in 45-minute blocks, and 15 minute breaks), time for non-study (and ideally doing something that will keep your mind OFF the subject matter.)You've got the 'study' covered. Sometimes, the non-study is more difficult to identify and enact. This time might include: reading a novel, seeing a movie, seeing friends, family, etc. the more activities you can do away from study, or the farther you get your conscious mind away from the GMAT, the more rigorous studying you'll be able to do. The brain actually integrates and problem-solves when its not actively working on questions, so this is good for your overall study regiment.
2. FOCUS ENHANCEMENT. There are many ways to increase focus. These include, but are not limited to, meditation, yoga and mental exercies that enhance focus. Most are easy to do, but you need to do it, consciously, as often as possible. One exercise we perscribe is called Focalized Listing Exercise.
At least once a day (but ideally 2 or 3x), write down a list of 10 - 30 new things you notice, either in your house, office, when you go out, etc.. Your items could be anything at all -- things you hadn't noticed before as well as, nuances of color, texture, form, shape, sound, smell, etc. Keep the list going over the next 3 weeks. This activates your being PRESENT and the more present you are, the more you'll be able to relish in the details, which mean, you're staying in a FOCUSED state. The more you're able to keep present, the easier it is to enter back into this zone, and for longer each time. Our students hand in these lists - - then we know they're doing it. Feel free to send them to a friend or even me, off line, each day - - I may not comment, but at least you know someone is receiving them. Practice makes...well, you know...perfect.
3. RELAXATION. Relaxation is key to peak performance. You can relax several ways: finding music that is gentle and flowing (without lyrics, even), stretching, walks, getting out in nature. You can also listen to our sampler. It's free...put on a headset and listen. There is actually a few minutes that have focus material, so that will get into your mind as well.
There are infinate ways to bolster focus. There are just three quick ways to harness this intention.
Studying for the GMAT is not only about mastering skills, it's also about engaging your strength, courage, and confidence. Focus is part of this, and it's very trainable to be your best self on the exam. You've felt focus before...now its time to re-call it.
Good Luck!
