New St Augustine Sod in TX

2 1/2 months ago I had St Augustine sod laid down. We had 2 days of rain and my grass was beautiful until the heat hit us....near 100 every day which in late late May was higher than usual temps. I have been watering with an isolating sprinkler and at first I was watering 20 minutes every day. I was watering either in the day or evenings. When the heat hit I noticed my grass suffering. I read and finally I had a lawn care person pay me a visit. I was told by the lawn care company that my lawn was suffering from "burn" believed to be by the sun and she told me not to water during the day. Instead she told me to water at night when temps were over 80 and in the mornings when temps were lower than 80. I wanted to get some advise here. I have St Augustine in jn back yard and I water it at night, maybe 1-2 times a week and it is beautiful but because this is new grass I was trying to make sure it had enough water. It is completely rooted but I definitely have brown spots now which the lawn care company did not feel were a pest or fungus issue. My question is how often do you suggest to water in temps near 100 and do you suggest evening watering like the company suggested to me?

Okay, the first thing I would recommend is that you read https://permies.com/t/11/organic-lawn-care-cheap-lazy or at least the article it is discussing. There's watering, fertilizing, and mowing suggestions.

My St Augustine is thriving just following the mowing instructions. I don't water or fertilize my grass at all. In fact, I occasionally steal nutrients from the St Augustine by bagging the clippings to mulch other areas of the yard that need a boost.

It seems like the biggest limitation the St Augustine in my yard is sun exposure. Maybe if I watered it would take over my whole yard, but instead it gives me dense green coverage everywhere that gets at least some afternoon shade. I think it spread into  my yard in the first place (before I moved here) from the neighbors, as there is an uninterrupted section from the shade of their live oak to the first trees on my property.

As for watering at night, absolutely. Plants basically stop all biologic function they can manage over a certain temperature. (I think it's usually 90 degrees) If you water at night in Texas, this gives the plants the absolute best chance to absorb all that water before it evaporates, runs off, or the plant stops functioning. It's colder climates (or maybe in the winter) where the water will sit and stagnate that watering at night causes problems. Their nighttime air is too cold and humid to evaporate and can develop into mold and disease vectors on the plants. Not a problem in Texas.

St. Augustine is a fairly water hungry grass plant, if you want it to grow lush, you need to water it for no less than 1 hour per watering, less than that and you are encouraging shallow roots that mean daily watering will be necessary.
This is a rhizome grass so you can get a very nice play area with it just by doing the things necessary for the plants to do their thing.
Getting the soil biome healthy an thriving also keeps you from having to water much if any, since the water will soak down and the root systems will also grow deep to access that held water.

Casie gave great advice too.