I didn't bother looking there as the manual stated its options were "Language", "Units" and "Default Panel". I checked the maintenance mode menu on my current printer and there is no option for auto power off.
Bummer. It would have been a nice feature if I knew how to control it. Wish one of the two Epson techs knew aboout it. Would have saved me a lot of trouble too.
Strange that the Epson site lists the available firmware as the initial release on Oct 2009. No updates are listed. Just curious, if you don't mind, what firmware version is your 3880 running, Menu/Pinter Status/Version. Mine is P0079C-1.03.800E.