We change to standard on the way up at transition altitude, but on the way down we switch to QNH as soon as we get cleared to an altitude with a QNH. The standby altimeter however is set to QNH until TOC, then its set to standard, as soon as we get the ATIS of our destination its set to QNH again.
Transition Altitude is mostly around 5000ft at our usual destinations. Small european outfit, formerly owned and audited by BA.