I have not been able (because of other health issues) to take any of the stool softeners for constipation. In your opinion is there any reason PJ would not be ok to drink with AF? I still have not found a doc that will do an exam without my first having a colonoscopy but I'm still trying. This is a stressful situation. Thanks.

Yeah prune juice is ok to drink as far as I've seen. I just started drinking it a few weeks ago (omg it's disgusting), but I also take a stool softener and miralax, so I think for me it's overkill and I don't notice any differences. But yeah, I wouldn't worry about drinking it. (Just from researching it online, I'm not a dr ;) )

When is the best time to drink it, relative to BMs? BMs are a morning thing for me, so I was thinking of drinking it at night. Does it actually soften, or just induce BMs?

I drink mine in the am about an hour before breakfast. I started with 1/2 cup prune juice mixed with 2 oz apple juice (to make taste better) + little water. I think it taste better to drink it hot with a straw. If 4 oz doesn't do the job go up to 6 ozs. the next day or dose.
I would try it when I didn't have to leave the house in the mornings. When you feel the urgency you definitely want to be near the BR.