I would suggest until they are room temperature and have a little time to rest with the little end down and big end (air sac) up, for about 4 hrs but not longer than 8. I don't know all why people suggest doing this, but I have heard that it is to do with the air sac sometimes will burst into the albumen and this gives time to allow it to recollect to the big end of the egg. My luck with shipped eggs is that if you can see bubbles moving around, the egg is likely not to be any good...but really why not at least try anyhow. I never really checked if they were able to recollect, I just wait until they have had time to sit out at room temp next to my incubator for about 4 hrs then place into the it to hopefully be firstly fertile, then grow and hatch.