How often and at what time does the guide do major updates? if it does...

I suppose this thread could have gone in the more active Roamio thread, especially since I have both, but I'll give it a try here, although the answer is probably the same across all Tivo platforms.
I like to manually look through my guide Sunday mornings and have noted if the guide has updated quite early Sunday morning, say 5am ish, if I do a manual update at say 10am, it downloads quite a bit more information. As I no longer have dial-up I can't go off how long it takes to download the...

How often and at what time does the guide do major updates? if it does...

How often and at what time does the guide do major updates? if it does...