Interesting, I did not know that and I raised Pheasants and wyandottes for years. How much slower for the brown egg to drop compare to a white egg ? Are we talking minutes, hours or day??
I would say for Marans egg productions you get 4-5 eggs a week as opposed to white leghorns that will lay everyday for 10 days.... but some of that has to do with breeding for better laying. Marans tend to lay in cycles, really well for a couple of months then slack off for a few months.