With some subjects its never late to start from reading from scratch even a few days before the exam. But it would requires one to put much effort and focus. I am speaking from experience,i read from a text book all the semester’s(four months) work in about five days. 296 pages,Entomology. Hahaha,or should i say crammed? And i did ace the exam. I have always been like that ever since primary school. Always been surviving, and with flying colors. Now about to go for my masters. So i can say my ‘never too late’ depends on one’s area of study (subject);one’s ability to stay focused during those few days to exam left;how sharp the brain is; and willingness to work very very hard. But i advise you to stick to your notes as they save you time and torture to your head from things (abundantly found in ‘that’txtbook / on google)that may not even come in the exam. Good luck