Cramming is not a good idea in any upper-level discipline. Even for the brightest of the bright, the most important piece of the learning experience is time. If you give yourself one night, there's no time for the information to soak in and really be retained. As far as chemistry goes, you need practice (which takes time) to either learn the process or memorise everything you have to do.
On the other hand, the physical sciences just don't come to some people :/.