Ticket machines seem to have strict time restrictions on. Once at 9:58 I tried to buy a YP discounted ticket from a ticket machine when the next train was at 10:07. I had to wait for the time on the machine to get to 10:00 before I could get one. Normally ticket office staff at small stations are happy to sell you an off-peak ticket as soon as the last peak train has departed. I'm not sure what happens at big stations when they can't keep track of when every train leaves.
I found this out for myself when I tried to buy a G M Evening Ranger at 1816 at Manchester Piccadilly yesterday, in readiness for using it on the first tram which turned up after 1830, However the guy in the ticket office refused to sell it me and said the rules were that he could not sell me one till 1830.
I then asked him the question what if someone wanted to get an Evening ranger to travel on a service departing at 1831
and after three attempts at getting a response to my question, he gave me the answer
"Tough, they'll have to get the next train".
If I had been wanting to travel on a train timed to depart at 1831, I probably would have gone and spoken to the conductor of the train,however I wanted to travel on the Metrolink so had no choice but to wait until 1830, thus missing any trams which departed between 1831 and the time I subsequently arrived on the metrolink platform.
I find this slightly unacceptable, as it's valid from 1831, yet I was being prevented from potentially using it as such.
If this was advertised as such on Leaflets and on the Nationalrail website then it would be acceptable,but it's not as if I haven't bought one at Stockport, around a similar time in the past and used it on an 1831 service.
On that occasion all they did was remind me of the restrictions and I stuck to them, as I have always done, since I have no intention of having to pay a standard fare, whether it be an Anytime ticket on a train or a £100 fare on Metrolink,simply because I did not buy or have a valid ticket.