I have always had issues every now and again with EPG updates keeping the receiver awake. I think using OpenTV you are more likely to see this, you could try using rytec providers instead, because I think this does the update while the receiver is in standby and for some reason the OpenTV can wake the receiver up, not all the time, but never found a 100% reason why it happens.
I prefer to use OpenTV - so I have used various ways to put it back in to standby. The method I use at the moment is menu - setup - system - AutoShutDown settings, and I keep AutoShutDown disabled, but enable action after activity - set this at 120 minutes, and for it to go in to standby. This will put the receiver in to standby after a 20 second warning if you haven't pressed anything on the remote for that length of time, can get a bit annoying if you don't channel hop much but it is ok for me.
There is also a plugin called Buyukbang from the ViX feeds - with this you can run a daily scheduler that returns the receiver to standby at any given time each day, or you can schedule it to reboot after an EPG update with the same tool and return it to standby - not fully tested this plugin but it is worth giving it a go.