Every UK Apple Store, green the moment a real check sees your chosen product in stock for pickup today - amber when it’s tomorrow pickup only. Nothing estimated.
A store lights up only because a real check against Apple’s own pickup feed saw the product there. The page re-checks every minute while open; availability can change between checks, so confirm on apple.com before travelling. “In stock since” is when one of our checks first saw it in stock - a store we haven’t checked recently may have restocked earlier. Checks are cached for up to two minutes.