What is the most productive review source for internal medicine recert boards for those short on spare time?

Internal medicine. Try MKSAP review books. This will prepare you pretty well to sit for your internal medicine boards. Good luck on the exam.
Cramming. Hi minikelly1, I found that mksap16 worked the best for me. It took me about 2 weeks to run through all the questions and explanations. It is high yield and updated to the current testing. Hope that helps.
Medstudy. I think medstudy is the best resource I used for the board exam. Mksap q&a also was helpful but textwise, medstudy gave the most info in shortest amt of words. Good luck to you.