Since the whole "daylife" phenomenon erupted several years ago, pool season has elongated with each successive year, as both pools and patrons seek to stretch the party opportunities to the max. Back in 2012, a forecast of rain and snow didn't deter Mandalay Bay's Beach and Moorea pools from debuting the first weekend of March, while last year Sapphire gentlemen's club's new Dayclub was the last man (woman?) standing, with its final party taking place as late as October 21. As you noted, official auditions for "team members" kicked off in late January this year, with Rehab at Hard Rock, Tao Beach at Venetian, and Marquee at Cosmopolitan already having held their casting calls.
That said, the reality is that the effects of global warming have not yet had such a radical effect on our local climate that basking by the pool is likely to be a desirable option within the next few weeks, and while most major hotels maintain at least one heated pool year-round and Mandalay Bay continues to fly in the face of (possibly) freezing temperatures with a March 7 "daylife" season debut, calls to Rehab and Artisan's Naked pool revealed more civilized kick-off dates in mid-April.
The bottom line is that March is a notoriously fickle month when it comes to temperatures: You might just get lucky with a mini heatwave, in which case you should be able to find a pool to hang out at, whether at your hotel or at another that welcomes non-guests (these days many do, albeit usually for a fee -- see our Cool Pools feature for listings of these, plus topless pools, poolside gaming venues, and more); on the other hand, you could find yourself battling driving rain and lows in the 40s, so our best advice is to pack a balaclava along with that bikini, so you'll be ready to weather the weather, whatever that weather may be!
As an aside, since the demise of the Tropicana's indoor/outdoor venue several years ago, there's no longer any hotel-casino with an interior pool, but there are a few non-gaming properties which offer that amenity. Check out the Question of the Day Archives (5/23/2013) for a complete list of these, plus details of all the indoor public pools around town, should actual swimming, as opposed to sunbathing and partying, be your priority.
