Well, during recidency you study for multiple things and not all resources are equally efficient at preparing you for the different "obstacles" or goals that you will have.
Also, not everyone absorbs information in the same way. My advice, and what worked for me pretty well is as follows:
In services + IM boards = Use MKSAP + UWORLD Qbank for IM boards. You don't really need more than that provided that you concentrate in what you are doing and absorb the knowledge reasonably well. Within MKSAP there is a billion different "mini" resources, I am only talking about the questions, flashcards and MKSAP textbooks and all that is nice to have but the efficiency of those resources to boost your test-taking skills just isn't worth it.
For everyday function as a resident (and attending in the future). Uptodate. Anything that is your bread and butter you must know like the back of your palm pretty much within the first 3-6 months of internship. After this, those bread and butter (CHF, COPD, DKA, etc) should not need you to review every time you get an admission. However, anything a bit rarer (SLE, Vasculitis, Mycobacterium Marinum infection, etc. should prompt at the very least a review of the main Uptodate article, and that applies to everytime you get one of those admissions that you have not seen in lets say 6 months.
Finally, there is the expansion of your general medical knowledge, bragging rights among other residents and attendings, and continuity of medical education. For this, subscribe to any one journal (just one, you won't have time to be reading dozens) and make sure that at the very least you read the first page of any article that applies to your specialty. I like NEJM.
As for how much? Well, i'd say 15mins every day regardless of how tired you are. That should be about 10 questions if you are doing a Qbank or 1 article otherwise. If you have downtime (you were done with your notes, but you are still on call waiting for your next patient and you are just checking your facebook, then do 30mins of studying first, then do whatever you want). If you get at least 2days in a row, I'd say 1h extra for that week (either during your days off, or if you really really want to relax or travel or something, then you find a way to study an extra 1h through the week in exchange for the days off.
Honestly, that + a half-decent, or even mediocre, residency should prepare you well for your in-services, boards and attending/fellowship.