The airing date will be measured by its initial "Aired" date in its MyAnimeList entry: https://myanimelist.net/anime/54857/Re_Zero_kara_Hajimeru_Isekai_Seikatsu_3rd_Season

The market will resolve YES if it begins airing on or before June 30th, 2024. The market will resolve NO if it hasn't begun airing as of July 1st, 2024. The market will resolve NA if the third season's production is cancelled (and not just delayed) on or before June 30th, 2024.