You can at least schedule a download to start at a certain time ("Run at") when you have selected the set for download.
Then I guess you can either manually pause it in the morning if not finished, or kill the urd daemon from cron tab
You can also start it from cron, and if you have checked the setting to resume jobs after crashes it should continue when it starts up. Less than ideal perhaps though.
A somewhat nicer way would be to have a cron job that adds/remove iptables rules to allow/disallow access to the news server at certain times.
Without knowing for sure, it doesn't sound too complicated to add a global native setting for when urdd is allowed to use the network. If it's not already there it will probably get added eventually.