According to ESPN reporters Adrian Wojnarowski and Zach Lowe, teams around the NBA are expecting June 1 to be the date the league calls back players who've left their home markets since the season abruptly shutdown in March. Teams also expect that same day to represent a point in which they can ratchet up the intensity for workouts for players who are already at team facilities.
While these presumed developments don't appear to lend themselves to an exact date on which you can expect regular season games to start again, it would be a publicly visible sign that actual actions are being taken for the league to return in the relatively near future.
As Wojnarowski put it:
Furthermore, The Athletic's Sam Amick and Shams Charania have reported that Disney World in Orlando, Florida, is being heavily considered as a "frontrunner" site for games if/when the season returns. Also up for consideration, at least when it comes to proposed cities for a return, is Las Vegas:
We'll update with more information if it becomes available.