Some recent studies have suggested that 8 hours sleep each night is possibly too much and that 6 hours is a better figure to aim for.
When I was younger I hardly needed any sleep. (In my early twenties, when I first started teaching, I went to bed for three hours on a Tuesday night, three hours on a Thursday night and 4 hours on a Sunday night. Those 10 hours per week were all I needed and, given that it usually took me an hour to get to sleep, my actual weekly total was probably closer to 7 hours).
These days I tend to be semi-nocturnal. I went to bed at 6am this morning and got up 10 hours later at 4pm. However it had probably taken me 2 or 3 hours to get to sleep, so my total time sleeping was possibly around 7 or 8 hours.
My sleeping patterns can be very irregular though. I might stay up for 30 hours and sleep for only 3 or 4, followed by being up for 20 hours and sleeping for 12.