Might be down to allowing fans a bit extra time to get to the ground. My Sister lives around 5 miles from the Hawthorns and the roads around there, particularly on the nearby M6 are very busy. The game is also on Sky ( red button), so it might be to fit in with their schedule.
The matchday programme at the weekend said 7:45 pm. Then again it still had Bristol City down as 3 pm a week on Saturday.