5150,
I do know the FCTM...
What I mean is that I know of no airline where it is SOP to engage autopilot on its minimum engagement altitude.
Remember that automatics can do faulty things, and that the autopilot is prone to "peculiarities" on the classics.
That said, in environments like JFK, Heatrow etc. I put on the automatics after 1000' as this is our company minimum, but keep guarded yoke/throttle until 10.000'.
Never put full trust into automatics, and remember, if in doubt what it is doing, disconnect and fly the aircraft.