Wait until the leaves die, the vines shrivel and the stems dry. When harvesting, don't cut the stems. Instead cut the vines, leaving just a tiny bit of vine attached to the stem. If frost is coming, harvest.

I was referring to the Carnival squash. I figure pumpkins are mostly seasonal decoration. I harvest them when they're orange and I need a jack-o-lantern.

tcstoehr's advice holds for all winter squash. Carnival is an acorn type. For good quality they must be mature. If you don't want to wait until the vines die back, at least wait until the skin is hard and dry as well as the stems.
Big Moon is a show variety, much larger than the average Halloween pumpkin. They have been known to reach 200 lbs. If they are staying golf ball size after the bloom fades, you have pollination problems. They size up fast.

Hello,

I guess to clarify, should the Big Moon pumpkins be yellow as immature fruit? I've always seen pumpkins be green as small fruit. I am concerned I got the wrong seeds.

Thanks for the carnival squash info!

That I don't know. I don't grow Big Moon and while there are lots of pictures of the mature pumpkin, I have not found a photo of an immature one. At any rate you will have to go with what you have at this point.