***** NOT A TEACHER *****
1. I believe that the complete sentence for analysis and diagramming is:
"In a second study by the same university, around half of 2,000 women who were polled admitted that they spend more time
looking at women than they spend time looking at men."
a. As you said, "do" is a substitute for "spend time looking at."
b. As you said, the purpose is to avoid repeating "spend time looking at."