I only had 3.5 weeks total as well to study (didn't prep at all during MS-3 year, but did do almost all the UW IM questions). I tried reading some MTB in the first few days combined with UW blocks, but didn't feel that I was retaining much of what I was reading (plagued with short attention span here). For the second 2 weeks, I focused entirely on UW and went through the entire questions bank. Currently on my last few days of prep, and am doing a grand review of the notes I took + marked/wrong questions + a bit of MTB skimming for the heck of it.
