There’s another factor involved, too … avast has shifted a great deal of its def-updating process over to the streaming updates, which don’t trigger any popup. So if you’ve got streaming enabled (I think that’s the default setting now, anyway), you’re probably seeing fewer “regular” updates than in the past.
Those streaming updates are quite frequent, nearly continuous … if you look at the updates info where David referred you to, you’ll probably see that the most recent one was only a minute or two ago, as compared to the latest “real” version which is typically a few hours back.