Summarize this article:

This allows the curls to cool and hold their shape. For softer curls, you’ll only need to wait roughly 5-10 minutes, depending on how thick your hair is. For super tight, bouncy curls, wait at least 15 minutes. To see if the foil is still hot, lightly touch it with your finger. If it’s still warm, wait a few more minutes before checking again.
Wait 5-15 minutes for your hair to cool and the curls to set.