To be fair, I also wouldn't date someone who said, "Not now, but later." If someone I'm interested in can't give me a 100% yes, it's a no.
It wasn't literally that phrase, of course. I don't remember the exact phrasing, but the first answer in the list was like "Hell yea", the second felt to me like "I'm interested but give me some more time". I didn't expect that to cause the door slam shut.