The hours are because the people there go to car shows and participate all season.
Monday and Friday are travel days.
This isn't a static display with cobwebs and dust, the cars run, go to meets and people there are avid fans.
All the more reason to go and support it.
I was there when a new car (the Champion) arrived from the shop.
It made the 1/8th mile trip on an Isetta rollback, very, very cool.