off peak train tickets?
 

when exactly can you use an open off season return train ticket?

It varies depending on the journey and can also depend on the direction of travel.

As a general rule of thumb, trains BOTH IN AND OUT of a major population center will be "peak" between about 7.30 and 9.30am. Trains OUT of major population centers will also be "peak" between around 4.30pm and 6pm.

But basically you need to ask.

Go on trainline.com it will show you off peak trains and times