Is there a specific reason you want to take it in January as opposed to later? There really is no reason to try to rush your studying and preparation for the MCAT.
It is possible to jump 3 pts in that time, but it depends on why your scores are they way they are and how much time during that month and a half you're committed to studying. If you can identify certain "high-yield" areas where your score will improve if you bolstered up those areas, then it's a bit easier to increase your score. Also, if timing was an issue and you just need to take more practice tests to get the timing down, then that can help.
You should be able to make more than a 3 point jump in that time if you are very focused on high yield study habits as Rutgers stated... check the 30+ thread.
Alternatively, you can easily get PS/BS scores to 10-11+ if you spend a few dedicated weeks to months on those sections and preparing very well on practice tests. It may be better if you take more time studying to boost your score to a 30+, because you are certainly capable. If you are not hitting 28-30 by test time, I would suggest not taking the exam. It is nice to be scoring a few points above your goal prior to test time, and you can do that if you work hard enough.
Depends on how much time you put into it in the next few weeks. It is definitely possible. In my opinion there is typically a very dramatic jump in scores once you finally begin to "get" how the mcat questions. I studied everything one time through and my score went up a little. then as I kept going back through everything, ESPECIALLY the concepts behind everything, and as I took more and more tests, I got a good feel for the test. My score then went up a good 3-5 points in a matter of a few weeks. So it depends on how familiar the material is to you already and how much time you are willing to put into it.
I would suggest no less than 5-7 hours a day until then if you are serious about it.