I find sleep to be a changing state of affairs, some weeks I seem to need as much as 15 hours on occasion this seems to coincide with periods of minimum activity.
However if I have some form of project in mind, (I was going to say in hand but the innuendos would have been rife!), I find I can go with very little sleep in fact at such times a couple of hours just resting as Gayle said will be sufficient.
Before you ask no! It's the latest style of water bed very relaxing.