This is basically you are talking about scan operation on covering index i.e non clustered index .I have video on that .please check it out. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-yefP63XqlpY.html
Time taken to complete operator execution. If you are running query "select * from tablename" and if see execution plan for it. You will see different boxes. These boxes are called as operator and if you hover every operator you will see different matrices such as estimated cost , actual cost and many more.