Many of us think we have figured it out, all by ourselves. We know, empirically, what makes us tired, how and when. And we assume the rest of the world works the same.
Well... - it turns out that there is a fair variation across the population, and in order to really know how people in general are affected by work and rest periods, time of day, sleep debt, workload and acclimatisatpon, we need to rely on quality-assured science. However, studying up on this science can be quite difficult - and at times it may seem that there are sooo many different results and interpetations out there - even conflicing ones.
If you recognize this description, it may be of comfort to learn that there are a fair number of findings that a good portion of the scientists DO agree on. Findings found true, over and over. The Working Time Society have put great effort into summarising these in a number of consensus papers and made them freely available. You can find them through this link. Enjoy!