It varies a lot depending on how people did in their courses. If you made high grades throughout the core science classes then you can probably take a practice exam or two right off the bat to identify weak areas and then only do the full review of those things. If you aren't especially strong or weak in any certain areas then try something like SN2ed schedule where you rotate among each subject, doing about 1 chapter of each content review per day
For me, I probably spent 4 weeks of 4-5 hrs/day in content review, mostly in physics and biology, and then 6 weeks doing weekly full lengths and reviewing what I messed up in each section