I had read of many guys claiming they could leave their guns over a period of time. After spending 6 hours at the range (longer than I intended) I swabbed my barrel with 2 wet patches (both sides) followed by 2 alcohol swabs (both sides), and assumed I'd be good until the next day after using Pyrodex after spraying it liberally with WD40.
I found out this wasn't so for me. I live in Texas, and it was fairly humind (not so much in the house). It rusted my barrel fairly well, and was a pain to clean less than 24 hours later.
My stainless pistol, using Triple 7, was the opposite. It handled it well, and has always been easy to clean regardless of powder used.
But I also found the rhythm to cleaning a barrel much quicker, and maybe my process wasn't quite as keen. Now it won't ever need to wait.