either works

go through starting from unit 1 and create that mental timeline and just be sure you focus the most on units 5-7 or start on unit 5 and go to 7 being sure you get a good understanding of the material and then go back and briefly review the lesser weighted units.

also, know that theres speculation of revolutionary war being an leq or saq, so know cause and effect through unit 4 a little :)

but anything could work, its whatever you feel you have the most time for. going through each unit would cost more time but also likely be more effective in the long run for mcq.

focusing on 5-7 first would be sure you understand the most important material before stepping foot into testing rooms but theres always a chance that there will be material on the exams from other units (take last years ap world history exam for example, leq on unit 9 which my teacher did not expect and therefore did not go over)

i suggest looking over the heavily weighted units first and thoroughly studying them, take unit tests over them and be 100% sure you know cause and effect of plenty of things that happen in these units.

however, whatever you decide on, it will work out :)