I've crammed for exams my entire career as a student. I had a good undergraduate background in the sciences, so that probably made it more manageable for me to cram than for some of my classmates who were not biology majors or only took the bare minimum coursework in bio during undergrad. However, after every single exam, I regret cramming because I basically spent a week sitting on my butt all day. I wouldn't recommend cramming even though it works for me, because if you want to do well you will be miserable for a week straight before every exam.
In terms of the number of hours studying, I agree with previous posters saying that hours don't matter. What matters is if you are studying effectively. So many of my classmates try to learn every last detail of professors notes. I think that is ridiculous and boring. Rather I try and get a big picture view of what I am learning and the major points and then fill in small details I could get tested on. The only two classes where my method didn't work well is biochemistry and pharmacology, which are more like straight up memorization classes, IMO. Do what works for you, but if 6-8 hours studying a day isn't cutting it, then try a different study method.