Right. Sleep consumes the vast majority of that. Then, if kids are in activities after school (band, sports, clubs), subtract even more.
Both of my sons were HS athletes. They would be home for 30 minutes awake in the morning before leaving for school. Then 8 hours in school. Then typically 3 more hours after school in practice, lifting, traveling to and competing in games. Many days (especially game days), they would be gone from 7AM until 8PM, but most days gone from 7AM until 6:30 or 7.
During the school year, gone for 12 hours, awake at home 3-4 hours.
The impact was less in elementary and middle school, but regardless - the impactful "awake" hours are massively influenced by their in-school time.