Does it taste good? If it does, I wouldn't mess with it regardless of whether it sets up or not. A flavorful syrup is always better than an overcooked or rubbery jelly.

Keep in mind also that a jelly can take as long as six weeks on the shelf to set, so what you're seeing now, not even 24 hours in, is no indication of what you'll be looking at down the road.

Carol

I made some cinnamon plum jam last week from overripe plums. They were so sweet that I had to add extra lemon juice (even Dave will let me get away with extra acid!) and I used Pomona pectin with minimal sugar. The following day it was syrup, but a week later it set up just fine. Tastes good, too.

Plums are quite high in natural pectin and shouldn't even require SureJell, so it's hard to imagine it wouldn't set up with the commercial pectin added.

Of course, knock-on-wood, commercial pectin isn't 100% reliable, but usually that's with a low-pectin preserve like a pepper jelly, not plums.

Carol