I say spend most of your "study time" studying for step 3 and just get it out of the way ASAP so you can spend the rest of your time reading EM related stuff.
Let's face it, that's really what you're going to be worrying about. Every time you read some EM text, you'll be worrying about when you have to take Step 3 and whether you should be doing questions or not. Just get it out of the way so it's not a distraction any more. There's a lot of medicine minutiae and other stuff on that test that is quickly lost the further out from med school you are, and isn't really stuff we think about, or at least think as deeply about on a day to day basis in EM.
Just read what you can, when you can. As mentioned, uptodate or reading brief snippets about something you're treating in the ED is a quick way to learn and helps you retain. As Arcan mentioned, it also depends on how busy you are in residency. Last year, I think we averaged about 18 or maybe 19 12 hr shifts and I honestly gave up on all my Rosen's scheduled reading assignments about 3 months into the year and started using other, more brief and concise texts simply because I didn't have the time to read everything. That being said, I feel like I saw ALOT of stuff in the ED and was actively reading stuff about it while I was treating it, so retained and learned more than I thought I would after that year was over. After reading the 1000 questions book for our ITE, I was surprisingly much more prepared than I thought I would be.
This year, I'm working fewer shifts and will prob have more time to read. Just do what you can and pick a text or review book that doesn't put you to sleep. Rosen's is like benadryl for me, I'm out after 5 pages and don't recall anything I just read.