The magic number

[Camron Rust]

The violation should occur when the clock says 25.

I think all shot clocks work the same: they remain on 35 until 1 second has elapsed...the horn buzzes as soon as it reads 0 (not 0.9999 seconds later).

When the clock shows 35, between 0 and 1 second has elapsed.
When it shows 34, between 1 and 2 seconds have elapsed.
Taking this down to 25, between 10 and 11 seconds have elapsed.

35 => 0 - 1
34 => 1 - 2
33 => 2 - 3
32 => 3 - 4
31 => 4 - 5
30 => 5 - 6
29 => 6 - 7
28 => 7 - 8
27 => 8 - 9
26 => 9 - 10
25 => 10 - 11
24 => 11 - 12

Therefore, if you wait until it says 24, you give them at least 11 seconds and, depending on your reaction time, up to 12 seconds.