Could I brew up a batch of beer, cool it, then leave it in my chest freezer with temp controller overnight and pitch the yeast the next day? how soon do you really need to pitch the yeast?
I do it all the time without issue.
You need to pitch the yeast before something else has a chance to build a strong colony in the wort. That means the amount of time you can wait depends at least partly on your sanitation. I’ve gone as long as a day and a half while waiting for the yeast to be ready from the starter, but was pretty nervous. Turns out I was fine. Overnight I do occasionally but in general I try to make sure I have the yeast ready to pitch for brew day.