Well, many here will say that you should use 4F in your pan. Their line of reasoning is that it is "faster" than 3Fg in the pan and tests seem to bear this out. How much faster? It seems to be a few thousandths of a second.
On the negative side of this question many others will point out that 4f powder will "turn to soup in the pan".
I ran my own test on this "soup" question and it turns out that under some conditions the accusation is right.
If you are interested in my "soup" tests follow this link.
THE 4F SOUP TEST
If you don't want to follow the link, the bottom line is that YES, if the pan contains fouling the fouling will attract moisture from the air and that moisture will contaminate the 4F powder making it unusable as a prime.
In a clean pan (with no fouling whatsoever) the moisture will not collect in the pan and the 4F will remain good.
As to the question about going several days without shooting a flintlock there have been several posts about this question.
Most of them seem to end up saying that if you dump the pans prime and plug the vent hole with a suitable plug (stick, feather, tight fitting tapered metal pin etc.) the main charge in the barrel will remain good.
Repriming in the morning will get you back in hunting condition.
This assumes the patched ball is a tight fit and does not use a watery lube that will contaminate the powder after several hours have passed.
IMO, anyone who is thinking of leaving their flintlock loaded overnight should treat it like it was fully loaded at all times, even with the "vent hole plugged".
The reason is that if the plug should fall out for any reason and if one tiny little spark gets into that open hole the gun will fire.
Also, if it is cold outside do not bring the cold gun into a warm place like a tent.
Condensation will form on all of the metal parts and it may work its way into the vent or thru the patch in the barrel. If it contaminates the main charge, all bets are off and the gun will likely misfire.