If you are using the saltpeter, you could brine for 21 days, but the longer you brine the saltier it will become.
If you are using cure #1, you should keep your brining times as close to 3 - 4 days as you can, but if you have to go longer; I would not brine over 10 day; 14 maximum if using cure #1.
The better choice would be to delay the start of the curing process, so that the end of the cure time is much closer to the time you are able to smoke/cook.
Either way you cure, after removing from the brine you should not refrigerate over 7 days before smoke/cooking.