domain date.io

Good keyword, decent extension, I think with the right marketing you could sell it for a decent price.

Agreed. It's short, singular, lots of commercial/online appeal, and multiple uses/meanings.

I would aim for five figures right now, and be happy to sit on it until the right buyer (end user) comes along.

I suspect you would get close to four figures if you auctioned it on Flippa or Park.io.