I normally do them after I've left the last station on the trains journey. However this is not always easy as a lot of our blinds have completely broken and just display as blank. This is due to the new 'easy winding' installations on the refurbs of our 153s and 156s which fell to bits pretty much as soon as they were put in.
Yeah when ever i go spotting to Lincoln, i get the service from Doncaster and its already set to Lincoln, but that will almost certainly have been changed at Gainsborough Lea Road. Most of the EMT services into Lincoln are already set to there next service on arrival. I have noticed there are so many different blinds on the EMT units, theres two units kicking around with black and white blinds think its 153381, 153385 and 156414. Then the rest either have Black and yellow ex CT blinds or blue and white EMT blinds, but now EMT have some more new blinds blue and white which are fitted to 153311 No2 End and 156413 the lettering is bigger and wider and easier to see.
I would say the blind could be set at the last station before the terminating one, depending on how far you have to wind from one destination to another. If the EMT easy winding system is anything to go by its harder to change the destinations that what it was before.