Working nights I asked myself the same question and I have found the following numbers
About one-fifth of employed Americans work most of their hours in the evening or night, or have a rotating or highly variable schedule. Many more work some of their hours, but not most, in the evenings or at night. About one third of employed Americans work Saturday, Sunday, or both weekend days. Together, about two-fifths of employed Americans work nonstandard schedules. Men are somewhat more likely than women to work nonstandard schedules, and minorities—particularly blacks—are more likely than non-Hispanic whites.
I guess that for more information you will have to look at the U.S census bureau
Good luck