Hiya,
With usenet speeds, they will go as fast as the network will allow after midnight. So basically that means if the network isn't full, you'll get it as fast as possible. However, it will still be prioritised below Gold & Silver trafficv, so it mioght not run at line speed straight after the midnight kickoff period.
Bear in mind there will be a large number of other people who will schedule their downloads to begin at midnight.
