I'd ride my instructors new horses as soon as they came in. The only reason they may have been given time to settle otherwise, is because there may be a health issue to worry about, or if they came in in the middle of the night and no one may have been around to hop on.
My horses (if I had any), I would ride as soon as I could. I wouldn't go to a new trail or a new show ground, and wait around for them to look around from a stall. I would ride them, or at least, lunge them. Get them out where they can see things, get their feet moving. Let them eye ball some stuff, but remind them they still have an alpha and rider to pay attention to. Give them something to concentrate on other than blowing up, and make it a good experience.
See boy, there's the wash rack! The tack room where your stuff goes! Your new neighbor! Oh look, a round pen and arena! Why wait a week to fully introduce them to their surroundings? Why let them see things from a distance as they walk from stall to pasture or stall to arena, and only introduce it to them as you need it? If it is part of their new surroundings, get them out to it. They won't die if they see a bunch of new things on the same day. Horses are not that fragile.
Think of it not as a failure but as a success in how not to do it.
Don't look in a horses mouth for a gift.