Set the timer to close the pop door after dusk, not at dusk. Give them an extra 30 minutes or an hour after.... whatever works.
Either way the door to the run will be closed and secure before dark so even if they do get locked out of the coop. They will be safe in the run.. worst case scenario.
You made me think about this a bit..
The timers I've installed are programmable. That enables me to have as many opening and closing times as I want each day..
If I am getting a hen that is a repeat offender, I could add another open/close cycle that lasts for 1, 2, 3 minutes.. an hour or two after dusk.
This is all in theory because my coop is still under construction and my chicks are only 3 days old...
I'll post if I have any issues.
Edited by G-Man - 3/28/12 at 10:26pm