I 'need' about 6 hours but I can make do with less for a week or so. It doesn't bother me if its broken up into smaller chunks either which is handy when I do on call
occasionally I like a 9 or 10 hour session to blast out any cobwebs but its rare with Siobhan and of course now Joseph....
I do find that sleep when tee total does seem more valuable than when its after a few shandies...