I started off with a low, low AAMC 3 of 20 as my diagnostic and if you're in any situation like me, maybe my insight will help you decide when you should take the test. I'm scheduled for the October test date which gives me less than 2 months to boost my score up. It's been over 3 years since I took my science class and probably 6-8 years since I did my core classes so most of the basic sciences are in the way, way dark part of my brain. I spent June-July doing content review using EK books but I studied on/off..not consistent 6-8 hrs a day like other people did. If you plan to use EK books for content review, I highly, highly recommend you do your passage practice with TBR since EK is so concise they only give you the main info so you're missing out on other info you may need for which TBR practice will come in handy because you will learn from your mistake. If you miss a lot using TBR bio, don't worry because it's brutal and TBR does go overboard with Bio so just don't freak out if you only get like 1 right out of 7 questions.
In August, I started doing VR practice..this is one section that you will need to consistently practice since your score is a 5. Don't give up..just keep practicing and figure out where you're weak at whether it's your timing or inability to understand the passage or just don't know how to answer the questions. I started practicing with EK and TPR and saw my score go from AAMC 3 VR of 6 to 8-11 range with the prep books BUT when I did the AAMC 4 VR, I only got a 7 (1 pt improvement with 3 weeks of consistent practicing). What went wrong? Could be number of factors in my case: a lot of background noise while I was taking AAMC 4, not used to the format/style of AAMC, etc. Either way, even if you practice with EK 101, do not neglect to take AAMC tests every week leading up to your test date (don't waste the AAMC tests either if you're not ready) because I found AAMC format to be a bit different than EK and TPR but that could also be because I was nervous even though it was still only a practice test. Other people may have different opinions but from my practice, I like TPR > EK 101 > TBR/Kaplan for verbal...I feel TBR/Kaplan verbal is only worth doing if you run out of material...just my opinion.
I don't know how much time you can devote every day to studying for the MCAT or what your target score is or how you study. For me, I needed extra time to really go over the content because I did my science courses a while ago. You may just need some refresher and all the knowledge will flow back to your head. Also, I would recommend you purchasing the Self-Assessment tests from AAMC so you can take those after you finish your content review. That should give you an idea of what you need to work on. You can only take the tests once so to make it worth it, don't take it when you're "almost" done with content review..do it after you're done and feel pretty confident with the content. Another tidbit, in my TBR books I have a total of 488 passages for all subjects and my plan is to finish at least over 400 before I take the test so you may want to plan out when you plan to finish your content review and when to start practicing with an idea of what you plan to practice (which prep books) and so forth.
Lastly, since you don't plan to apply until next year, if you feel you can't get through the content and get some practice in before Oct 25, it's not a bad idea to postpone. Depending on how weak you are on your content, giving yourself some extra time isn't a bad idea. The most important advice I can give you: Don't let studying for the MCAT consume your life..give yourself a little break after studying and take a day off once a week to reboot. The first 3 weeks in August when I started practicing/reviewing content, I studied 6-8 hours every day 7 days a week and by the last week, I was just out of energy plus allergies and body aches were making it really hard to focus. Don't force yourself to study hardcore every single day because you need to take some time for yourself to do something you enjoy before hitting the books again.
