Security Scan Time

My full security scan starts at 20.00 hrs daily.I cannot seem to change this as there are NO scheduled task times set.

Is this some kind of default time?I have set a scheduled task for a different time hoping it would over-ride the 20.00 hrs one,but it does not,it just scans twice,once at my scheduled time and still at 20.00 hrs.It really slows down the PC when it scans in the evening when we use the computer the most.

As I am not a pc geek or anything,can some one help me out please in removing the 20.00 hrs scan then I can set my own scan time when no-one would be using the pc