Hello Tia,
Pods take between 30 and 90 days to mature (hot / cold weather and variety)and nearly all do turn brown when they are ready to drop their seed. You will see colour change and splitting of the pod whilst still a little soft and you can remove the pod at that stage if you like, but best to let it dry off for another day or two, watching it does not suddenly spread wide open as seed may drop (a sunny, hot can cause this).

The getting hard stage I presume you are referring to the pod reaching full size prior to the development of seed to maturity. It starts out after pollination at just a couple of mm then as it matures over time, grows to become between 10 and 20mm long. It takes a couple of weeks to get to full size and then will just remain unchanged until seeds are mature and pod begins to change colour and open up. Their is no time factor during the day applicable to when the pods get hard, but I suppose at the end of a hot day the pod could appear to be much more ready than in the morning.

Good luck.

Regards, Brian Kerr.