Virus Scan—P’s Internet Security—How Long Should It Take? OS Shut Down or Restart.

A day or 2 ago I started my first full computer virus scan after installing Desktop 4 and P’s Internet Security. It ran for about 36 hours and over 40,000 files before being interrupted by a computer restart, when it automatically restarted a scan. It’s not clear whether it started a new scan or resumed where it had left off, but it’s now at 24,000 files and about 20 hours.

How long should an initial full scan take?
Am I correct that subsequent scans should be much quicker?
Do I have to pause a scan before shutting down or restarting the OS to permit the scan to resume where it left off, rather than starting anew?