The plants will tell you. First they will BLOOM, so you’ll know there are taters below. Then the plants die back of their own accord (mine usually die back in August, Zone 5a) whether you’ve been watering or not. I stop watering after the plants are done blooming.
When the plants are pretty much gone, you can dig your taters. If you want baby taters, wait until after the blooms fade, then dig some. De-lish! :)
And they’re not particular. You can leave them in the ground (or pot) up until a hard freeze as long as they’re not water-logged.
So if they never bloom there won’t be potatoes? I’ll have to check it.