Norton Antivirus- idle time scans

Hi,

My wife does not like to have the Norton Antivirus running when she is working on her laptop. She will work for a few hours and then stop for a while.  So, I set it to run 'idle time scans' .  I have set 'ten minutes' as how long to wait till it starts.  Yesterday, I noticed that it waited the set time and did a Full Scan reporting about 750,000 files found before it finished.  I used the laptop for a few minutes and then it was idle again.  The scan started again and this time reported that it found 250,000 files before it finished.  Is this the way it is supposed to run?  How many times a day will it do a scan?