Someone who overestimates the time it will take to do something or go somewhere. The opposite of a chronoptimist.
"I was always such a chronoptimist when it came to sex, though. I'd need to be home at 12, so I figured I'd swing by his house at 9, but we'd be done by 9:30."
"Uh, I think you meant chronessimist."
"Thinking I had more time for sex? I'd say that's pretty optimistic."
"It takes me 15 minutes to get home, but she wants to me to leave now to be home at 3. It's only 2! She's such a chronessimist!"