I need to have 40 eggs pop onto a field, each egg is on a separate layer. Is there an expression I can use to do this or is this best done manually? Thank you.
Why bother? Just 40 eggs?! Writing the code and copy & pasting it to the relevant layers will take just as long. Simply animate and copy&paste the keyframes.
You can copy and paste the keyframes and then use the Sequence Layers command to get them to pop on in order. (There are scripts out there like Rift to randomize this sort of thing. And I think the RD scripts collection may have a free one that does it too.)