Tabebuia tree in trouble

My Tabebuia tree of 12 years does reasonably well, although the leaf tips are always brown. The tips are now black and a few small branches look dead. It is planted in an area surrounded by jasmine ground cover. It receives 6 minutes watering three times a week; total 18 minutes weekly. Is this too much, too little? "Black Thumb" needs advice, please.

P. S. I could not figure out how to attach a photo taken with my iPhone.

Here is my Tabebuia photo.

I'm in Long Beach and I have a Tabebuia on the parking medium in front of my place. Mine is doing the same thing as yours right now, probably due to the heat. It always does this during the summer when it's in the 90's.
"IF" yours shows these same symptoms year round, your soil and water may have a high salt content which can cause leaf edges to "burn".
Sometimes you can correct that issue by a DEEP watering every so often...to leach the salts out of the soil. The burned leaves won't recover, but the deep watering can help prevent it in the future.

Jasper, many thanks for your comment and advice. Will try a deep soak for my tree.