I?ve read references in several books (most recently, Daniel Quinn?s
Ishmael) to the ?fact? that ancient hunter-gatherers only worked three
hours a day and had abundant leisure time. I?m wondering: 1) What is
the basis of these claims? 2) Is that 3 hours spent gathering food or
3 hours doing all the things necessary for survival? 3) What is meant
by ?leisure? in this context? 4) If this is based on a study, does the
study have any scientific credibility according to today?s
anthropologists?

I suspect that the original source of this factoid is Marshall
Sahlins' "The Original Affluent Society" (I think in Stone Age
Economics 1972) which discussed two hunter-gatherer societies, the
!Kung San ("Kalahari Bushmen" who live in Botswana, Namibia and South
Africa) and Australian Aboriginals.  As far as I know, this was
perfectly good anthropolgy, and indeed the !Kung part was updated by
more work in the '70s sometime (by Richard Borshay Lee).

This site has quite a good discussion of it, albeit a bit shrill in
places, and answers some of your q's above, although you'd need to
read Richard Lee's book for a full answer.  (You'll note that Lee is
quoted as calculating a 40-45 hour working week in total in his later
work).

http://www.primitivism.com/primitive-affluence.htm
http://www.amazon.com/gp/product/0521225787/103-3713372-1064662?v=glance&n=283155&v=glance
http://www.eco-action.org/dt/affluent.html

However, the data has been extrapolated too far IMHO; we should remember that
(a) this is based on only two societies, and I suspect it would be (or
maybe would have been) reasonably easy to find counter-examples of
societies living in more marginal conditions where much more time was
consumed by finding food - for instance, people living in the far
south of South America
(b) although present-day societies may shed light on what the
societies of our ancestors, it is dangerous to assume that (for
instance) the 1960/70's !Kung San economy was exactly the same as the
economy of humans living millions of years ago, and
(c) the society of the !Kung San is very different today, and it is
very difficult to disentangle whether this is entirely due to
persecution by the Bantu-speaking majority and white farmers.  This is
a reasonably balanced article
http://www.villagevoice.com/news/0014,schoofs,13803,1.html

So as with most things, there is something in it, but it's been hyped
too much.  Not surprising, perhaps, as Sahlins' book was in itself a
reaction to the view that the hunter-gathering life was a constant
desperate struggle.
http://www.primitivism.com/original-affluent.htm
Wikipedia is also interesting on the subject:-
http://en.wikipedia.org/wiki/Hunter-Gatherer

I'm not a Researcher of course - I answered this because I thought you
had to know to search on Kung San to get started.  If you like the
answer you could donate your 30 bucks to the earthquake relief effort,
if you liked.  Maybe a Researcher can add more stuff anyhow.