Hartford and New York are about 100 miles apart by road. Split the difference and you arrive near Philadelphia, the city closest to the halfway point between them. That puts roughly 3 hr 47 min of driving on the Hartford side and 2 hr 1 min on the New York side — the fairest single meeting point among the cities near the middle.
At this range, Philadelphia works for a same-day meetup: close enough from both Hartford and New York to meet for lunch or an afternoon and still be home by evening.
If Philadelphia doesn't have what you're after, Boston and Washington are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Hartford and New York.
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.