It can depend on the heat, weather, and pests you have. If you have stink bugs and lots of rain around, it's better to pick it sooner and let it ripe in a bag or something.

Otherwise if there is nothing attacking the fruit, I leave mine so it become dark as possible. It can get quite dark and very sweet, but it's somewhat prone to cracking.

Thanks max they are kind of dark now and I tried to pick it easy to see if it would come off like regular cherry tomatoes but it seem to be attached still pretty good. I have no trouble with bugs or rain because I grow them in straw bales so water is not an issue.

I think it is a trial & error process - early on - we had a hard time waiting to taste them (first year we grew Black Cherry too) and probably ate them before they were ripe - they tasted good anyway. We let them get darker and they tasted even better! We are happy with the Black Cherry tomato - they are good sized with great taste!!