And while the second question is stupid IMO since that is up to the manufacturer to decide, the DFDRs I'm familiar with are turned on when you turn an engine on since you're not too interested in recording half an hour of setting the switches right. If there's a complex hyd system with electrical backup pumps I guess it could be of interest to have a bit of recording going already on power up, for troubleshooting if nothing else.
Cheers,
/ft