This is a unusual time to start a game considering most other sporting events start on the hour, or at quarter past, half past or quarter to the hour.
But in the USA, it is actually not too strange as it's been the case for a long time.
It is because in the US, broadcasters that start at 8pm are allowed to have a few minutes build-up, analysis and an advert before the game.
Also in that time, the national anthem is usually sung and the opening ceremonies or ceremonial first pitch take place.