Much of the length of time depends on a number of things;
Patch Lubes
1). Patch lube (water based is the worst for causing rust).
Weather
2). Weather - the temperature your hunting in that may draw moisture into the patch material (again causing rust).
Rust
3). You do not want to "ring" the barrel. The rust ring where your patch sits when loaded, some materials (metal) of barrels differs, the softer metals will rust faster and deeper than harder materials (metals).
Had a few guns traded in - finding the rust issue when cleaned, looking at the bore by pulling the breech plug or using a bore mirror will really show what is going on.
Loaded
4). Have had a few rifles that have been loaded for several weeks (forgotten) then cleaned and found there was no issues. These guns had been left in dry storage was the only reason we could thing of for still being OK. My brother-in-law (know better) left a TC Hawken for 4 years then asked if I could get a replacement barrel as he figured it was now junk. One afternoon I we pulled the nipple put 4FFFF in the hole then reassembled and fired the rifle. Shot fine but when looking down the bore it looked pretty sad. With a little fine grit valve compound it cleaned up using just the ramrod and jag and an hour labor. He got off lucky that time.
Bottom line is weather and temperatures, you need to try your best to keep moisture out of the barrel and the ignition system. There have been some really good ideas posted on here about keeping the ignition dry, I'll let those that have to fight this answer these issues. :ttups: