I answered and there was nothing on the other line. I suspected some sort of robo-call, as most delays like that indicate that it takes a moment for the caller to realize that somebody has actually answered the phone out of the many that are attempted. After about 10 seconds, I hung up and looked it up here. As I suspected - some sort of spam/marketing thing.
I answered to know who the caller was. Tried to sell me solar panels. Said I wasn't interested and hung up. Caller ID said call came from Gladsboro, NJ. I live in CA.