"Unique circumstances regarding the growing season, the fruit variety or the fruit itself occasionally necessitate more than 24 hours for a gel to form. Therefore, wait two weeks to see if the product will gel. Do not disturb or shake the product during this time."
So maybe it will set in the next two weeks. Either way, I think I will always perform a gel test from now on, just to make sure before I process jams and jellies.
Apparently you can also remake jam that is already cooked in order to attempt a better set.