Do you still have time to memorise the important concepts? You know how much your science teacher loves KEYWORDS!
Do you still have time to practise some questions?
The answer is NO.
You cannot spend majority of the time reading the textbook the day before your exam. Some students might not even be able to finish reading it in one day and they start to panic even more. You should be reading your textbook, summarise the key concepts and write your OWN summary notes way before the exam!