Everybody feels sleepy while the Sun is in the 8th house, it's a rule.
Best moments for study - I have a very extensive experience observing these moments for many years and I wrote these observations in an article titled "Ciclurile intelectuale" (Intellectual Cycles) for Astrele (nr.7). The image below is taken from that article, it is not perfectly accurate to describe what I had in mind as I intended to represent the astrological houses containing the Sun and not actual zodiacal signs, but one can easily understand it using the house-sign association.
Also, the hours are just raw approximation, as the timezone, the location and the daily variations will change the exact moment when the Sun enters the next astrological house.
But one can get a pretty good understanding of the best time intervals for study from the graphic below, as from my observations:
Best moments to study new subjects: "air" houses (11, 7, 3); best moments to get a better grasp on subjects already studied, to review knowledge - "earth" houses (10, 6, 2); best moments to get the bigger picture, to draw synthetic graphics, sketches - "fire" houses; best moments to go for a nap - 'water" houses - 12, 8, 4
I also wonder why the examination sessions of college students usually take place while the Sun transits the intellectual signs: Aquarius, Gemini and Virgo - this is no coincidence.
As for sports, I think the Sun in the 7th house is perfect for team sports against an opponent (soccer or any other), while the Sun in the 5th house is perfect for fun sports (including venereal sports).