Attempt GMAT official Guide Book Multiple Books

Is it ok to attempt the book multiple times? Sure. Nothing wrong with it.
Will it help increase your overall score? I doubt it. Doing the same questions again and again won't help much. You need to understand the concepts of the questions you are unable to solve and then try different questions based on that concept. Redoing the same questions serves little purpose. You can perhaps redo it once after a few days to ensure that you do understand it properly now.

Time you need to spend over the weekend - very subjective question. Depends on what works for you. Many people preparing seriously for GMAT with a full time job try to put in 2-3 hrs every weekday and 6-7 hrs each day over the weekend. Though how much time you invest has little relevance. How you use that time productively is more important.

Again 8 hrs a day for 2 months doesn't guarantee a good score. It's fine if you want to get done with it soon but you must understand that you will have to take interest in the topics tested. You can't just skim them, do a 100 question on each and expect a great result. You need to know exactly what is tested and where you stand. Then you need to focus your efforts on topics that give you problem. You should also take a mock CAT every 10-15 days to evaluate yourself and learn how to manage time during the actual exam.