How are you defining this ?
Definitions get many updates per day, just look at the About Avast (right click on Avast Tray icon) and you will see in my case 230320-4 which means there have been 4 updates, there are times when this can be much higher and or lower than that.
Also note that you should be getting streaming update that are very small incremental updates to the virus definitions.
Just check the defs sub folder and you will see a _streams folder C:\Program Files\AVAST Software\Avast\defs\23032004_stream. These ensure your regular virus definitions are up to date until the next update.
