From the OFFICIAL LOTRO FORUMS:
Scheduled Server Downtime: 8:00 AM – 10:00 AM Eastern (-5 GMT) Every Thursday
In order to help mitigate some performance issues the team is working on resolving, the LOTRO Game Servers will be brought down each Thursday from 8:00 AM – 10:00 AM Eastern (-5 GMT) for a maintenance restart. Thanks for your patience, and we’ll see you back in the game soon!
This also announced HERE:
The Thursday restarts are only temporary. For example, yesterday we announced that there were New ISP Routes in Place. Our Ops team continues to work on server configuration changes, and our game engineers are looking at all options from the game coding side. Everyone here is committed to improving game performance, but in the meantime we have found that restarting the servers can help mitigate some of the issues that can pop up.
And this announced HERE:
They are not automated and require staff to be on hand to make sure everything comes back online correctly. We thus have chosen the time based on the lowest populations during hours that are reasonable to ask staff to come in at and is the same time frame that we normally choose to have down times for maintenance, updates, etc to maintain consistency.
The weekly restarts should only be a short term occurrence. The main purpose for the restarts is a bug that should be fixed with Update 18, thus once that is out these should not be necessary.