Drying time is very much dependant on the weather and air flow- could be two weeks or two months. Very important it is dry though and you won't know until the doors are closed and the sun has been on it- shouldn't smell badly enough for you not to be able to breath it. Best to leave it disassembled as it will dry quicker. Don't creosote the perch tops- just the ends and bottom. Good to have the perches sitting in hangars so they can removed quickly for inspection, as that's where the red mite first appear.
I dilute creosote 50:50 with paraffin. It dries much faster and soaks in better without any effect on the anti-red mite properties.
Experience has shown me that it only works for a year. Problem is once you have hens you will need a spare coop to reapply the creosote and let it dry. Red mite normally arrive with new hens, so if you add to the flock that's when to expect problems.