The figure I saw (on the BBC article and the linked Swedish article) was 17,000 hours per year in this school.

That still seems suspect: estimating a school year of 35 weeks that's 175 days, thus 97 hours per day across all teachers. Even if it were some mega school of 1,000 pupils and maybe 100 teachers that seems high, would imply they spent perhaps ten minutes of every hour in a six hours day taking & dealing with attendance on average! (obviously based on assumptions, so this could vary)

It feels like a number that was come up with (or at least inflated) to justify the project.