I raised this subject before in the context of the machines at Vauxhall (which are standard so I assume it applies elsewhere) which won't offer an off-peak ticket until 09:30, meaning that any passenger using the system who is unaware of the rules but who is intending to travel just after 09:30 will only be offered an 'Anytime'. I happened to notice this morning that my ticket emerged from the machine stamped 'printed at 07:55 .....' just as, twenty feet above me, the 07:58 was departing. So, presumably, if I was turning up later I would not be able to purchase an off-peak ticket until 09:33 or so.