OP, I work as well, though not nights, and am taking 2 classes. I'm shooting for the 5/27 MCAT. Yes, preparing for it is challenging, mainly in an "energy managment" way.
Here are some suggestions that I'm trying myself:
1) Do you have any breaks when you work---10/15 minutes here or there? Can you review flashcards, or do a passage, or listen to some AO? Conversely, what about diligently using breaks for energy management---take a walk or do some stretching if you've been sitting, or sit back with closed eyes and do some deep breathing, or listen to your favorite music (either that perks you up or calms you, or whatever)? If you've been inside, can you go outside for some breaths of fresh air? If you use your break for a pitstop, what about splashing some warm or cool water on your face? Brushing your teeth might be helpful, too (it is for me).
2) I don't remember if you mentioned what type of work you do. Is there anyway you can relate anything on the MCAT with your work? For example, my work includes a lot of reading, so sometimes I think of what I'm reading in terms of a VR passage---what's the main point? What biases does (or might) the author exhibit? If I take the author's position and extrapolate/apply it to (some topic, like health care), what would s/he think? Or if you work in a research/health care setting---does anything you deal with allow you to relate bits of it maybe to anything in Bio---what do you know from Bio that would help you think about the patient/research you're working on? What from physics? Anything from Gen Chem or O-Chem?
3) During breaks/down time, pull out a practice problem/passage you've done recently that you bombed or aced. Now that you know the right answer/s if you didn't already---if you missed a question, how could you have figured out the right answer? If you got it right, is there any way you could have figured it out faster? Regardless, what's the shortest way to the right answer, and does that way make sense? Why did you miss the question, if you did? Make a note/flashcard of the fact/concept/definition/relationship/whatever and glance at it a couple more times during work.
4) If there's a fair amount of time during your work hours when your brain isn't actively engaged in work, do you have MCAT stuff in formats you can use? For example, if you are lifting and moving stuff and it's not very dangerous, can you listen to AO? Even if the MCAT today is concept heavy, it can be handy---pause it every now and then to relate what you've just heard to something you're working with right that moment, or to another concept from the MCAT (kind of like SN2ed's Hat Trick).
It's hard, but not impossible. For me, the hardest thing is being efficient: time/energy management.
Finally, re. that 4-day adjustment period. Please make sure that is a realistic adjustment period, given the nature of the adjustment and the possible stress/tension as you approach your MCAT. Is it possible to expand the 4 days, and would that help? If not, do you have a strategy for making the adjustment? Like melatonin and food, and maybe cutting back on caffeine NOW, so if you have to use some then, it will be more effective without giving you the jitters? Timing of exercise, waking, rising, etc? Just suggestions---I know for me, the better I plan, the better chance for success.
Good luck!
We can do this!