More accurately, it applies to journeys between 0430 and 0959 (inclusive) Mondays to Fridays
I've been meaning to come back to this for a while. I tried to get a discussion going about the new rule (between 0430 and 0959, rather than the previous before 1000) going
here, but nobody really rose to the debate!
In the end I left it because the terms & conditions on National Rail Enquiries seemed to suggest that the minimum fare applied to any journeys that involved travel between 0430 and 0959. But I was in England a couple of months ago and out of curiosity picked up a 16-25 Railcard Leaflet at Feltham Station and noticed that in there it referred to journeys
starting between 0430 and 0959. And indeed on the 16-25 Railcard website it says:
http://www.16-25railcard.co.uk/using-your-card/railcard-terms-conditions/ said:
A £12 minimum fare applies for journeys starting between 4.30am-10am Monday to Friday excluding Advance Fares. This minimum fare does not apply on Public Holidays or throughout July and August.
So, if these are the officially applying terms and conditions, then I believe
smith368 is actually correct in his interpretation that he can buy a ticket dated the previous day or earlier that is valid for more than one day, start his journey any time previous to the 0430 cut-off point (this could even be up to a month earlier, in the case of the return portion of a period return) and break it somewhere convenient. Then as his journey will have already started outside the 0430 to 0959 period, he will be free to resume it within this period and the minimum fare won't apply.