Does it do this when you just have it connected to the magsafe?
I am aware of that....
10 minute sleep and 5 minute turn off the display.
Still not sleeping
That really didn't answer the question...
I assume that you have the MagSafe connected from the 24"? I asked if the computer fails to sleep when the 24" is not connected and just the magsafe that came with your computer is connected.
check your power settings when plugged in vs not plugged in. They are different.