Planted them after the last frost date but they still hit flowering way behind schedule. Check your local climate guides, not just the seed packet, to nail the timing.
Wait, but aren't seed packets usually right on the money? They test them all over, so the dates work for most spots, unlike @jamesm38's cold backyard. I've always used packet dates for my beans and they come up fine, even in cool springs. Maybe the problem is not the timing but how you planted them or the soil itself.
Had a similar thing happen with my tomatoes last year. Got them in the ground right on time, or so I thought, but our spring was way cooler than usual. Forgot to harden them off properly because I was in a rush, and they just sat there for weeks. Turns out my backyard is a frost pocket, it's always five degrees colder than the front. Really makes you look up your actual microclimate, not just the town average.