If you used a neem product with a label on it for plant application, there would have been a clear warning about not using it in the sun, or when temperatures are very hot.

Most commercial Neem oil products contain 70% neem. I've never seen any directions that called for mixing it any stronger than about 2 tablespoons per gallon of water. It should never be mixed stronger than what the directions call for. Just as with other products (of almost ANY kind), more in not necessarily better.

Your label will also state how long you should wait before reapplying your neem. It does not work like other chemicals which need to be reapplied after a rainfall.

By the way, you must be cautious about spraying any chemical on your plants in the hot sun or very warm temperatures. Foliage or fruit burn is often a result.

I'd be quite curious about the product you used and where (on line) you found those directions. If you tell us the manufacturer, we can look up a label and help you decipher it.