I'm not a Daybreak employee but I did maintain a server for a while. It takes time to apply updates, change any parts, and other items that may not be able to be done while the game is running. They probably just apply updates and restart and test everything in a 2 hour window. The 4 hour or more is probably reserved for part replacement. Most servers are not like a regular PC, they have so much to load, it usually takes more than 5 minutes to do a simple restart. Then you have to think about doing it to multiple systems and testing to make sure everything loads back properly.
