Can a combination of watered plumerias and cool nights cause the death of them?

The days are very warm, even hot on my roof by day, to the point that they dry out fast.

But if a water that day and then at night it is very cool, am I asking for trouble?

Will the cool nights cause rot if they are watered although the nights get very warm? Are they still taking full advantage of the water in the soil with this type of enviroment?

Should I stop watering them, even make sure rain doesn't get to them when nights get below the 50's?

For instance, they were so dry this am the leaves were starting to droop in the hot sun. then I watered them. Now the pots are damp, and it will be in the 50's tonight...low 70's tommorrow...

Thanks a bunch everyone!