FedEx delivers packages on Saturday for sure but not on Sunday.
On Sunday the packages are still usually traveling through the FedEx facilities and are on trucks being shipped and planes as well.
But on Sunday the FedEx main drivers that deliver packages to homes do not work so you won't get a Sunday FedEx delivery.
I have had packages delivered by FedEx on Saturday before so that would mean that you might get a package on Saturday as well if you're expecting a package.
But if you don't get the package from FedEx on Saturday then it will probably be delivered on Monday.