The world still has some hunter gatherer societies living today, so studying them could give us some insight into how many hours our hunter gatherer ancestors worked.
The hunting and gathering (and storing, and shelter, and guarding, and...) surely were as varied as semi-modern (pre globalization) societies. The amount of work would depend on the natural environment and climate, hunting or fishing, trade with other local tribes, culture and mythologies.
I'd argue that the few, highly sequestered, remaining hunter gatherer societies, by virtue of being the only ones still around, are likely to be very much outliers in some dimensions and actually plausibly quite different from our own ancestors.