I don't know what the proper ettiquette is, but...

I'm a really slow eater, even slower if I'm having a conversation while I'm eating. If I stopped when the other party was finished, I'd often leaving the restaurant hungry but with a lot of food. I usually just say, "I'm sorry, I'm a slow eater," and go into the story of how we'd always made mealtimes at university last as long as possible so that we didn't have to study...and then I'd go home for breaks and my family of very fast eaters would lose patience with me and leave me at the table when they were done.

If I was your date, I'd want you to enjoy yourself...for you to eat as much as you'd like. Hopefully there'd be no rush to finish the meal, so...