That's correct, first weekend, but it's COLD! To me, the pools don't get good in Vegas til Memorial Day weekend. Thus, please see my countdown timer.
Average HIGHS 66 - 74 in March 1 - 31. https://www.accuweather.com/en/us/las-vegas/89101/march-weather/329506?year=2020
Most properties will have at least one pool open in March. The pool parties and dayclubs don't usually get started until closer to Labor Day, though. The weather is pretty variable. It was mid-30s and raining on Thanksgiving, followed by mid-30s and windy the day after, but it was in the 70s just a couple weeks ago. It's possible you'll get decent pool weather, but I wouldn't base an entire trip around that expectation.
Pool season is March is hit or miss. College spring break brings crowds but again things don't get crazy until late April