Interesting, I guess it depends on the client’s views.
I did some experimenting 2-years ago, I got mixed results. When I started selling my gigs, I delivered 24-hours delivery in the basic package, and yep, I got more orders (3-4 extra orders a mo), but they were from impatient clients. Then someone on the forum recommended me to change my delivery time to a couple of days, the number of orders was slightly smaller, but I got different clients, which were more polite (I did deliver in 24 hours though). Now because of the volume of the orders in my queue, and because I get more complicated orders, it’s not possible to deliver super-fast.
IMO, if you are a new seller, the 24-hours delivery time can bring you more work, but if you are established seller, it would make a small difference.