do you mean complete 5-7 chapters, or complete chapters 5-7? (gosh word order in english is so trippy)
if you mean completing 5-7 chapters, well it's entirely doable, lots of people have completed the whole course in the summer holidays (or so i hear). i wouldnt really recommend it though, because
a) you will forget part of what you learn
b) you will be so bored in class! whenever the teacher went through content i had already done, i would zone out and just scribble, and i would miss some of the finer details of the chapter.
c) its holidays!

doing so many chapters surely will take a lot of brainpower and time. it may be better spent creating a concrete foundation for all your subjects (unless this is your only 3/4). even still, enjoy the holidays while they last.
however, everyone is different and learns in different ways. to each their own!
as for the first sac: i dont know if its different for each school, but for us it was on the first 4-5 chapters.. all the chapters to do with functions: trig, modulus, polynomial etc. it was about 5 weeks in, iirc.