Amount of weeks is definitely important b/c it takes a long time for topics to sit. Also, it is extremely challenging to study more than 3-4 hours in one day. After that amount of time, your return on studying drops off. Also, if you go for 8 or more hours a day for days on end, you could easily burn out... I personally started with a 570 (absolutely NO studying) and ended with a 710. I work a full time job and studied for about 200 hours over 9 weeks.
Although this is not always the case, it is quite ambitious to want a 160+ point increase in 3 weeks. A 730 is the 96th percentile, and think about the talent you are competing against. You are trying to improve from a 58th percentile to the 96th...
Are you in a rush to apply? or just a rush to take the GMAT? It is generally suggested that you study over a 2-3 month period to reach your peak potential. I would not suggest that you rush the GMAT if you dont have to. Are you planning on applying Round 3? This is also a risk b/c round 3 is generally more competative. If you have more time, it might be worth spreading out your studying.
All that being said, there are numerous stories of large increases in a short amount of time. I would definitely say its the exception and not the rule, but you might be the right person to do it. I wish you the best of luck. Let us know how it goes! Good luck