Yes, this is normal to happen if the computer is going to sleep. In Sleep mode, only a few components are powered up to start rapidly, but the OS is not loaded, therefore the Scanning procedure is paused. That's why it takes so much to finish a scan for the whole computer. If it goes to Sleep it will never finish the procedure. Go to Control Panel and look for Power options. Increase the time until it goes to sleep and then start the Scanning procedure.