It’s got to be much further North than that. The train leaves KX at 11:00, there’s no record of it stopping anywhere, and it doesn’t get to Hogsmead until it’s dark. On September 1st, sunset is about 20:00 (19:52 in Didcot, 20:07 in Edinburgh), so if we assume it’s proper dark 30 mins later, that’s a journey time of 9 hours and 30 mins.
Let’s now assume an average speed of 40 mph, and that’s a distance of 380 miles. Which would be somewhere between Edinburgh and Inverness.
As far as water and coal is concerned, they are obviously replenished en route by magic.
While leaves as the only remaining issue the fact it’s not real...