Mince, I will wish you luck as it is terrible when you have a lot to do.
According to ancient folklore, if you went to bed before midnight, you benefit from the sleep twice as much than if you'd gone after midnight. So if you were asleep between 11 and 12 this would be the equivalent of two hours sleep.
I very often go to bed at nine and wake at around 1am feeling as though I've had a really good night's sleep.
Try your 12 - 4, and if you start to feel really knackered, go for an earlier sleep.