My Sony F717 also has auto-power off but this is disabled when I plug an AV
cable into the cameras AV-out socket and plug the other end into a TV or USB
video capture device. I assume it requires a load at the other end of the
phono cable so the camera can detect a current flow and keeps the camera on.
I'll give it a try without being plugged into a TV to see if just having a
cable plugged in is enough.

I *think* having the power adapter plugged in also disabled the auto power
off.

For shots longer than something like 1/20th (I forget the exact time) it
does auto-noise reduction/darkframing. The time taken to do this dark frame
is exactly the same as the exposure length. Which means my 30 second
exposures actually take 1 minute (30secs exposure + 30 secs darkframing).
It does this for very single shot which is a tad annoying as it reduces the
number of shots I can take by 50%. But it's still a nice feature to have
even if you can't turn it off.

Regards,
Ed.