One hour is absolutely ridiculous and I say that as a buyer.
I can't think of any business offhand where I would necessarily get a response within the hour.
You see the sort of nonsense from customers on marketplace occasionally, where they get angry if they haven't had a response within 5 or 10 minutes, but I didn't expect to see a big company like ebay jumping onboard with that.
Obviously, customers like a quick response.
But I think most are realistic enough to accept that it could well be several hours to a day before they get an answer. Most other companies I have had cause to contact this year have taken several hours to reply. (One took a week, which I thought was way too long.)
If I were still selling on ebay though, I would definitely try to have a 24 hour turn around or less for messages.
I know people work, I used to work full time when I was selling. But at the same time, most people can log on for a little while after work hours & quickly attend to business, if they need to.
As for whether the ebay messages about how long a seller 'usually' takes, and whether it could affect feedback. I guess it could, depending on the buyer. It wouldn't worry me if a seller with a 'usual' one hour took 3 or 4, but it could set up expectations with some, where they might judge a seller to be 'slow'.
It's about perceptions as if a seller had a 'usual' resonse time of 24 hours, then 3 or 4 hours would look fast.
