Yeah, going through whole books is very hectic and it can consume lot of time as well. One has to prepare 11 other subjects as well. As i am a vet doctor so biology was not a big problem for me,so i went through the botany and zoology books of F.sc in short time. But as far as physics and chemistry is concerned one should go through the "important" topics. Plus even if you cannot study those books, you can go through kashmiri's book/Dogar's book and those topics which are not clearly explained in these books, then you can consult F.sc/A-level books only for those topics.
Since its a high scoring subject and one can even get 80+ marks, so if you give it a little extra time in your preparation, you will not lose anything.
Regards