Not too bad now days with SSDs and fast boot, but back in the day that may have been a 15+ minute mistake. Getting into windows took several minutes and you would still have several minutes of nearly unresponsivness as background processes booted, including your anti-virus. Usually you clicked the power button and waked away for a bit. And the trick to speeding up your pc was to dig into the startup folder and delete as many programs as possible so they wouldn’t start at boot, because for some reason everything wanted to.