Very gently, squeeze one between two fingers. If it pops open, it's ready. I use a small glass jar to catch the seeds. There's enough room to get my big fingers and the seed pod through the opening. They're very easy to collect. You may even see a few pods split on their own. I find many pop when you touch them.

One of the few seeds that I know how to collect ") When the green bean lookin pod turns a pale greenish/yellow or brown, I hold it at the top between my pointer finger & thumb & slide down the stem, in my other hand I hold a foam cup under it to catch the seeds. They pop open very easily when their ready.
Jan ")