Generally i think they try to do them later, in the 2am window.. but have seen many reports of people saying 10pm+ (or even durring the day, if its a major update).
Unfortunately with these series boxes, there is no choice in when to do the updates. As well.. the speed of the box.. Thats a long, ongoing story as well. They tried to update and mondernize the guide a little. Unfortunately, the boxes are a little 'old' tech wise, and like running new software on an old computer... can be a little slow There is not a huge amount that can be done now.. its not like there are a lot of new boxes, etc too.. Cisco got out of the game for the boxes.. not many making boxes on that platform anymore
Most providers in canada and the US are trying to more over to newer stuff.. over to IPTV based services. Where there is much more technology advancements being done. Rogers new Ignite service is that way. The new box, you can actually CHOOSE the reboot/upgrade time!
But there are many things to consider moving to a new service like that (you can read up on the threads on the + and - of changing)