Sleep is incredibly beneficial for recall. Even a short dose of good sleep can really enhance memory. So, to set students up for an exam, I would advise them to study in the evening (on a decent meal, because we know that good food aids learning too – starvation is not wise), have a good 8/9 hours’ sleep, and eat a sensible breakfast (eggs and Omega 3s, if possible). Then they will be well primed for the exam situation.
The idea is that repeatedly revisiting ideas and concepts significantly helps to improve the durability of their retention. The idea is that the representation of that information drops to near zero, and then the process of reinstating that representation boosts its strength. Once this is repeated the end result is that the information is far more durable… than had you simply had all the learning in one block (without those ‘zero’ periods in between).