Can I "fill" a chicken pot pie 24 hours before cooking it?
Absolutely not. As the other poster said but I will say with no "I think", I will say I know it will ruin the pastry.  You will end up with a gummy crust that will never give you the flaky texture that pie doughs are famous for. It would probably also leave you with a somewhat dry filling as much of the liquid would then be in the crust.