If I were to guess, I would say that well over 50 percent of people that put out hummingbird feeders don't continue with it past the first year. Now take this information and apply it to how it would affect the hummingbirds each year. As millions of them spread across the country in their arduous journey, they are in search of food, of which much is supplied by feeders. Many of these first year birds are in search of new territories and nesting grounds. They will mark out new coordinates to get to these newly discovered places, and then return to them each year.
Now take this information and apply it to the practice where many people wait to put up hummingbird feeders until the birds appear at their window looking for them. It's highly unlikely that anyone will spend every minute of 16 hours of daylight, watching out their windows without taking a washroom, lunch, laundry, and appointment break. You are relying on these birds to be patient and wait for you in hopes that a feeder will be placed out, when over 50 percent of the population don't continue putting up feeders each year. They go through this on a regular basis, disappointment of no feeder hanging where it should be. Some may stick around, and many will move on.
Now here's my stronger point. This method of waiting to hang feeders until you see a hummingbird, is only catering to your regular population that know a feeder hung there last year. Every bypassing migrant is unaware that a feeder will be there at a future time, and doesn't have the slightest reason to stick around.
Trust me when I say this - the best practice by far is to have your feeders up and ready before they arrive. This rare Rufous, first time and first migrant to my yard in 2008, would have never stopped in had I not had my feeders up. He returned for 3 years.
There are NO BENEFITS to waiting until you see a hummingbird before you place out feeders.
N.E. of Edmonton, Alberta. 2008