I can confirm that holding down power on the Harmony remote brings up the dialogue, which is a problem, since automation of shutdown will require sending a sequence, deep standby followed by a confirmational OK. So far, I haven't even got the long power press to register as a command.
And whether a long press on the Humax remote works hit and miss. Sometimes I just get an ordinary standby, others, Android does a full boot, lasting maybe 45 seconds.
Ah well, life is too short for this, a schedule as on the BT Youview box would have been better than this faff, ie, deep sleep over a certain period, say at night.