All day long huh? I have heard that before but what they actually meant was a five round group. Very short day if you ask me. If a person can load/select their ammo to ensure that the velocity is less than a 25 fps std dev, guess the wind and hold consistently all the time with few or zero flyers then they can claim all day long.
I have witnessed good shooting in the past; such as a 1.9 inch group at 550 yards with moderate wind. That shooter never claimed to be able to shoot 1 moa all the time. When I see someone put thirty rounds into a 1 moa group, then I will not roll my eyes at the phrase, "all day long".