I got a 2012 11" MBA in Dec and it is hooked up to a TBD. A couple of weeks ago I needed something to download overnight so I set the sleep timer to never and forgot about it since so my mac has been staying on overnight (whenever plugged into ac and tbd in clamshell mode) for a couple of weeks. The screen was set to turn off at the default times thats why I never noticed it wasn't going to sleep since the screen would be off when I got to it in the morning and needed me to click the mouse to turn on.
I have been running on battery every 2 days or so and it did go to sleep in those times that I am not using it as a desktop since the setting only applied to when the AC adapter was plugged in.
I have been running on battery every 2 days or so and it did go to sleep in those times that I am not using it as a desktop since the setting only applied to when the AC adapter was plugged in.