8:40 used to be a standard curtain time in the 1920s, 1930s, and early 1940s. Much of the plot of Dinner at Eight hinges on this, and it's where the musical Life Begins at 8:40 gets its title from. I don't know precisely when curtain times were rolled back closer to 8:00, but it started sometime after WWII, around the time that the formerly urban audience was beginning to move to the suburbs and thus wanted earlier curtain times. We've seen that move even further in the last 20 years or so, as 7:30, 7:00, and even 6:30 have become standard curtain times for evening performances.
"You travel alone because other people are only there to remind you how much that hook hurts that we all bit down on. Wait for that one day we can bite free and get back out there in space where we belong, sail back over water, over skies, into space, the hook finally out of our mouths and we wander back out there in space spawning to other planets never to return hurrah to earth and we'll look back and can't even see these lives here anymore. Only the taste of blood to remind us we ever existed. The earth is small. We're gone. We're dead. We're safe."
-John Guare, Landscape of the Body