This is a great question and a concern for many students. In my own case, I took Step 1 after clerkships, and did not study for Step 1 specifically during, or prior to, clerkships. I think taking Step 1 after clerkships actually gives you a great advantage, as you have much more experience with NBME-style questions from taking shelf exams. I didn't review biochem during clerkships, and for me (and many of our students) its feasible to re-learn (or learn for the first time) the biochem you need for Step 1 during your dedicated period (mine was 7 weeks).

In general, I think its beneficial to have a longer (7-8 weeks) dedicated period if you're taking Step 1 after clerkships, as it will be difficult for you to study with significant intensity for Step 1 during those clerkships, and as you mention you will be further away from your basic science classes. However, we do have several tutors who scored 260+ on Step 1 with less than 6 weeks of studying after their clerkships. Try your best to ace your shelf exams, and this will end up being good preparation for Step 1 as well.

If you'd really like to brush up on biochem during a relatively light rotation such as psychiatry, I would recommend creating blocks of Step 1 UWorld questions with only biochem, and making Anki flashcards based off of the questions you get wrong, cross-referencing the relevant pages of First Aid as you do this. You may wish to read the Crush Step 1 biochem section prior to this, in order to re-orient yourself (this book has a nice narrative format that students find more readable compared to First Aid).

If you'd like more personalized advice for your individual situation, you can book a free call with me here: https://book.pocketsuite.io/book/usmle-pro-tutors