Perhaps you have a scientific basis for the time a "callous" forms, Hetty. My comments only relate to my own experience and I seem to have the same result whether the cutting "rests" for 24 hours or for several days. As long as that cut-end is hard and dry, I pot it. The only cuttings I have ever rooted that were more than 3-5 days old were those that I either had to cut to overwinter a very large plant, or branches that got knocked off when I was preparing my plumeria to bag them for winter.
Mike, Hetty is far more experienced than I when it comes to plumeria and I would follow her recommendations.
Ken
