They said it needs to be cancelled within 1 minute.
The whole point is, people make mistakes from time to time, and they must have the right to cancel a bet within a reasonable period of time.
In the case of a pub self help machine, where the user may not be familiar with how to cancel and therefore has to get help, 1 minute, or even 2 minutes, 3 hours out from race start, is not achievable. Even in a proper TAB, it would take longer than that to ask an operator to cancel a bet.