No more Mg. You have one "insulated" pot that I can see. That's the white-colored one, made of some sort of Styrofoam-like material. I have eight of those, four the size of yours and four twice the size. Those others are simply plain plastic, but that's OK, they will simply need watering more often. If it is sunny all day, I am watering all my large plumeria daily now and those that need re-potting, might have to be watered twice a day, which I am now doing. When those can get into larger pots, they'll only only have to be watered daily.
If your plants are getting sun from 1:00 till the sun goes down, that is actually the most intense sunlight/heat of the day. That pretty much means that your plumeria are in a western exposure. Don't fret that your plants are "only" getting 6-7 hrs. of sun. Believe me, they are getting plenty.
I re-pot my plumeria anytime during the spring and summer months. I simply do it when they "beg" for it which means when I am having to water more frequently than I want to do. I will re-pot at least 8 and possibly 12 plants late this afternoon and tomorrow morning. Keep in mind, that growing this heavy drinkers/heavy feeders in pots is far different than having them in the ground. The combination of lots of roots and lots of square feet of leaf surface, makes them transpire huge gobs of water and the hotter it is, the more they transpire. That's why intense sunlight and heat take a toll more quickly on the potted ones.