I did it during my lunch break ;) "Preparing to install" took 10 minutes (you can still use the system during this time) and the install itself took ~30 minutes on a 2011 MBA. Rebooted right to the desktop with no fuss.
Perfect! Did you have any services like postgresql or redis or anything that needed to be reinstalled?
/EDIT I just rebooted and my services were still present with no change. They had been installed with homebrew.