Tonight, close to midnight, I will be rebooting our primary web and ftp server. This will take about five minutes.
The reason for the boot is to load a new kernel that addresses some security issues.
The reason it takes five minutes is that this is a 32GB machine setup to make extensive use of caching in order to provide the fastest possible web response.
This means there is often much to be written to disk before a boot and that, even with fast modern drives, takes some time.