Time is ticking toward Sunday's 5 p.m. start of NBA free agency, which, judging from the excitement and speculative frenzy occurring on social media, has become pro basketball's Christmas in July.So far, depending on which media reports you choose to believe, the Mavericks:-- Have their sights set on Kevin Durant, Kawhi Leonard, Kemba Walker, Khris Middleton, Al Horford, Tobias Harris and Patrick Beverley, plus a handful of others.-- Dallas plans to meet with restricted free agent Kristaps Porzingis at the start of free agency and formally offer the five-year, $158 million max contract that has been expected since the moment the Mavericks acquired him from New York.