My wife has a saying: "As long as necessary". It's always suited me well...
When you say you're cooking/smoking at 265, where are you measuring (and with what)?
External mounted thermometers can easily be 50 degrees off (from where your meat
is located) in either direction.
Hance - Lake Dogs Cooking Team - MiM/MBN/GBA CBJ and comp cook
Lake Sinclair, GA (strategically about an hour from everywhere)