The Aircraft is fully powered by our Engineers before we arrive ALL of the time in my mob.
When the Aircraft terminates we don't power it down either ( we turn everything off but leave the power on ) Engineers do that after they finish their duties.
The only time we would is for an Un scheduled diversion to a port with no company Engineering support, then we could do it ourselves from the FCOM.
This is of course my Airline that only operates Wide Bodies. Friends in QF and DJ still power it up in the morning from dark in lovely cold places like Canberra and Hobart.
Nothing like a warm cockpit all ready for you.