Paul,

Its not Black tip, its probably frost/freeze damage. Usually when your plumies are exposed to frost or near freezing temps your plumie tips turn black, then after a few weeks or so you will notice cracking and splitting of the branches or trunk and black fluid that will ooze out along with shriveling branches. Keep an eye on the plants and I would cut off the damaged areas/tips.
Reds like Hilo Beauty, Irma Bryant, Wildfire etc., are more susceptible to cold damage.
Good luck.

I would wait and observe before doing too much more than cleaning off all the dead/damaged leaves. If the tip starts getting mushy then break out the clippers and cut back to clean wood. I use rubbing alcohol to clean my clippers in between cuts. IMO there is no harm in spraying anti fungal such as Neam oil if you want for preventative purposes.

My experience with light frost damage causing the tip to turn dark and seal over is it will either push out the seal (looks ugly) or start branches from the next nearest undamaged leaf nodes (still ugly to me). It will recover though. Here is a frost damaged Lei Flower Plumeria. You can see the damaged tips and how it pushed them out or branched. Also the first series of leaves and inflos on some damaged tips were misformed. It's since recovered.
{{gwi:1150452}}

Thanks guys! It's started to ooze some nastiness but I'm gonna hold off pruning until I note any mushiness or spreading of the black.