While the answer is difficult to ascertain, anthropological comparisons between farmers and hunter-gatherers suggests that the answer is rather close to 0.

Fun fact: hunter-gatherer lifestyles require far less work to maintain self-sufficiency than agricultural lifestyles. In fact, it wasn't until around 1900 or so that agricultural societies caught up to hunter-gatherer societies in metrics such as life expectancy and general health welfare.

What happens when hunter-gatherers and farmers come into conflict over land, which the latter utilize far more efficiently (in a calories / sq km sense)?

Note that as population densities rise, land becomes a bottleneck for a population more than number of available hours.