Say you don't want to download messages over 10,000,000 bytes long between 8:00am and 6:00pm. To do this, create a download rule as:
You also have to tell VPOP3 to Leave Messages On The Server for at least one day, otherwise the ignored messages will be deleted before it gets chance to download them.
That tells VPOP3 to ignore messages if they are over 10,000,000 bytes and the time now is between 8am and 6pm. Outside that time, VPOP3 will download big messages, including those that were previously ignored because of the time-dependant rule.