When to switch grit (from chick sized to 'big girl' size?)

[Life is Good!]

Any ideas when to switch the grit?

Our 8wk old Java's are between 1# and 2#'s (so getting bigger, but not the 7-9#ers they're going to be).
I'm nearly out of chick size grit.

Time to switch? Or switch when they get 'layer' feed at 20wks?

Thanks!

 

[hickchick55]

All I know is what I read on the "big girl" bag I bought this week. It said 8 weeks. My chicks have just been eating sand, but I was concerned that it was too fine.