Is it a done thing to do Competitor Analysis of a feature rather than a whole website?

I'm working on an e-Commerce site and have been tasked with improving their checkout and delivery experience. I already know who the direct and indirect competitors are. Because time is limited I can't do a full-on site-wide competitor analysis. Is it a done thing to focus competitor analysis in one area (in this case just the checkout/delivery experiences of competitors?). Any guidelines on this?