I would say take one every 3 days. Take one, and then two days to review.
Reviewing them was the most important part to me. This takes about a day if you review it completely, if you review the questions you got correct - which you should because sometimes you got lucky or sometimes you notice how you could have gotten that correct answer in a quicker way.
Also, I used to review the tests for a day, and then for a day id brush up on things i was weak on in the content books.
So itd be:
day 1: aamc practice test 5
day 2: review aamc practice test 5
day 3: go over some content from your review books
day 4: start all over
and i repeated the above for aamc practice tests 5,6,7, and 8.
If you have a "point in your MCAT studying where all you have to do is take practice tests", and you have all the aamc practice tests, then that "point in your studying" will take 3 weeks almost. Well, you dont want to forget the content during this period. So this is why i had a day in between (day 3 in that fake schedule abovre) where i reviewed content.