Studying for Step2 while studying for Step 1 is kind of like saying you want to apply for law school after medical school is over, so you're going to study for the LSAT with your extra time now. It really does make just about as much sense. Or maybe it's more like pre-studying MS1 material during the summer before med school starts - hopefully by now you understand why everyone says not to do that too.
Your thought process on time use is good, but the error is that the issue is not one of knowledge acquisiton but rather one of processing. The fact is that the kind of thinking you have to do for S1 questions is vastly different from S2. You need the S1 foundational knowledge to do well, but then you'll also need the experience on the wards and doing shelf exams to understand clinical reasoning and how you must approach those vignettes differently. It's not so much the conceptual knowledge is different, it's a switch in how you think and that switch happens less on anki and more in the context of actual clinical medicine. Making the switch early only risks costing you points on S1 and won't make any difference for S2 years from now when you finally take it.
For example: take something like the various antiarrhythmic meds. S1 is going to test the mechanisms, the underlying basic science, mechanisms, kinetics, etc. And all of that is important. S2 is going to expect you to determine which one to use based on the scenario, and that will be wildly different depending on whether its inpatient vs outpatient, ICU vs floor, hemodynamic stability of the patient, previously tried therapies, etc. And the answer may not even be a drug - may be a procedure or maybe you need more testing. The answer may be based on some RCT showing drug X over drug Y in that given scenario and have nothing to do with the basic science of it at all. There's no amount of anki cards you could do now that would prepare you to answer that, it's a process of clinical reasoning that you'll learn with time and you'll fit your basic concepts into it.
Focus on the task in front of you and don't needlessly risk a step failure. Any hour you spend on S2 content is either costing you points on S1 or needlessly risking burnout. You'd be much better served by taking those 3 hours and doing something fun outdoors, or even just taking a nap or watching a movie. Get your solid foundation now because I had S1 questions even on my ENT written specialty boards, so you know they must appear on everyone else's.
In the scored S1 days there used to be an old saying about what you need to prep for each USMLE exam:
Step 1: 2 months
Step 2: 2 weeks
Step 3: #2 pencil
The tests don't get easier, but the knowledge tested is finite and the more clinical thinking you develop, the easier it all gets. You'll have more than enough time to prep for and crush S2 if you put in the time and learn the foundational concepts for S1 now.
