I had an engineering interview in mid december mate.
Stay in your college the night before, i did and although i was the only candidate there and knew no-one it still turned out to be one of the best nights i had last year. Soo good actually that i slept straight past breakfast and was lucky that........
It starts incredibly late in the day-check in was at about 2 even though most of us had stayed the night before so don't worry about the transport.
We were given an hour long and slightly tedious talk about the layout of the course (BEng/MEng, modules, etc.) followed by a slightly innapropriate but interesting talk on F1 cars and we were all on edge at the end when he started asking random mechanics questions about the talk with us assuming it was part of the selection. Luckily it wasn't.
Then followed a 15 min maths test which i won't divulge on here but was much easier than we thourght and contained nothing beyond the OCR C3 module.
After a tour, it was now getting dark we went off in groups to rooms deep in the bowels of the buildings for 1-1 interviews. I say interviews what i mean is being asked why you want to do engineering followed by circa. 10 mins of We meet all those criteria and more at Durham, come here!!
The offer came through about 3 weeks later, probably would have been less but xmas was there.
I envy the fact that your interview will be post-oxbridge. Literally everyone i talked to had applied to cam and it was literally, "hi, [generic small talk] which college?", and as seemed to be more eyeing up the cambridge competition than trying to get an offer from durham.
After that it was a 9 hour journey home to the westcountry on many trains.
Good luck,
I hope you get in, i'll definately be going there in october!!