The NBA is targeting a December 1st start to the 20-21 season for numerous reasons, most notably to play on Christmas Day and also to avoid the Olympics.
If the NBA begins its season on December 1st, they can comfortably play an 82-game season and be finished in time for the 2021 Tokyo Olympics that begin on July 23rd.
But sources say the NBA could push back the start of the season if they're confident a delay would mean getting fans back into arenas for more games. The NBA could then take a month-long Olympic break similar to how the NHL has handled the Winter Olympics.
The Olympics could be deprioritized by many prominent players due to the pandemic and a condensed offseason between 19-20 and 20-21 due to the pandemic. This line of thought has made some within the league skeptical that accommodating the Olympics will remain a priority for the NBA.