It really is standardised, yes. A lot of people think the wrong dates were picked though, as the December switch causes issues for people booking train tickets for Christmas.

The Loco2 blog has a bit on how it all works, and for more detail try to find a talk by Mark Smith from Seat 61.

As for when tickets for next September come on sale, it'll vary, but no earlier than about May. Most of the rail booking systems in Europe operate with a 3 month horizon. There's some slight variation, but broadly I'd say you wouldn't want to look up September train times for certain until a month or so before the June change.

(For an idea of what'll be there, check for tomorrow, as the summer/autumn timetables should be similar for next year, but there's no promise it'll be the same)