When hawk watchers talk of an exchange, they're talking about the process where the male gives the female a break. When these start, it's usually safe to assume at least the first egg has been laid. Today, I was fortunate to see Pale Male give Octavia a break of about twenty minutes.
(The exchange was a little odd, in that Pale Male left the nest unattended for about four minutes. He may have been helping Octavia with a territorial dispute out of my view.)