It depends.
I stop when I have to add/remove clothes, when I have to pee, when I want to eat something more than an energy bar, when I want to take a picture, when I get to a red light, or when I get lost.
If neither of these happen, I don't stop. I've ridden 70km non-stop, and I've also stopped three times in 30km.
I'm not going to beat any record, so I stop whenever I feel like it.