what does "pancakes in the age of enlightenment" mean?

Basically means that in todays society because of all the stress and
fast paced ethics that have came to be that even a flat or dumb joke
can ease tensions or make someone smile once and awhile.

Old, old joke...

CUSTOMER IN DINER: Your sign says "Breakfast Any Time." 
                   I'll have pancakes in the Age of Enlightenment.

Variations: "I'd like hash browns in the Renaissance," "gimme waffles
in the Stone Age," etc., etc.

i know the old joke, but i was watching the movie "swingers", and he
said that his waitress wouldn't get the philosophical reference.
apparently, i didn't either!

A waitress who had never heard of the Age of Enlightenment would
probably not get the joke. I don't think there is deep meaning here;
the joke works just as well with other historical periods instead of
the Age of Enlightenment.

The wonderful deadpan comedian Steven Wright tells this joke often,
using "French toast during the Renaissance."

Descartes goes into a diner and orders a cup of coffee. The guy behind
the counter asks if he would like cream in his coffee. Descartes says
"I think not" and disappears.