I have marinated chicken overnight, floured it for frying and didn't cook. What is the best way to store it for frying at a later time?
There is no good way to keep it in the "ready to fry" state. I'd suggest to simply store it in the fridge as you would do with unfloured meat. When you take it out, just flour it again. The thicker flour crust will make it somewhat closer to a schnitzel, but it won't taste bad.
If you already had a very thick flour/egg/flour layering on it, it's probably better to wash it off and dry with a paper towel before storing, then redo the panading procedure for the next fry.
Actually, there is at least one Southern restaurant known for their fried chicken that leaves the chicken pieces in the bowl of seasoned flour (lot's of flour) over-night. It creates a drier coating and bonds the flour mixture to the bird and the very crispy crust does NOT fall off. Excellent!
Uncooked chicken breasts are really only good for 1-2 days in the fridge (assuming that they were thawed), and I wouldn't recommend storing them floured in the freezer. I think the most practical solution would be to fry or bake them, and then flash freeze them. You can reheat them in microwave or oven, and they will be as tasty as the day you made them.