Download Manager/NAV version update question

If using the Download Manager method to update the version of NAV2010 (either to the latest 2010, or to 2011), do you have to stay online during the whole install/changeover?   If so, how do you stay protected when it overwrites/crosses over from the old version to the new version.  Is there a window during the changeover in which one is not protected in real-time?  Thanks!