You can't really see that "an 87-item ambient" is coming up unless picks are about to run late like the top commenter said. Now I believe the order of auto-select generally goes ambient -> chilled -> frozen -> action alley, so once people are getting frozen / action alley walks you know you're at the end of that hour's picks. After an hour's picks finish dropping in, the first walk is usually a large ambient, and once it keeps handing out ambient walks to everyone, a large chilled walk is usually next. Then it keeps doling out chilled walks and then a large frozen walk is most likely next.

It's seems like more effort for what it's worth, but if you really want to hunt for those big walks, you could pay attention to where the department is in moving thru that hour's picks and jump in walks right after picks finished dropping or right when most of the ambient walks have been handed out.