The Lottery was planned for Tuesday, May 19th, while the Combine was scheduled for May 21st to 24th. The 2020 NBA Draft is scheduled for June 25th and has not been moved as of May 1st.
The postponement makes sense as the NBA figures out next steps for concluding it’s 2019-20 season. The lottery normally takes place during the playoffs, but the league suspended play during the midst of the regular season. NBA commissioner Adam Silver has been sorting through various hypotheticals for returning to play, and the postponement of the lottery suggests some kind of regular season return is still in play. The lottery is based on final regular season standings, so it is possible that could still change.
Silver previously said May 1st would be the earliest the league would start making decisions on the league calendar. Postponing the Draft Lottery and Draft Combine give the league some flexibility for figuring out next steps. It does not mean the regular season is definitely going to happen, but it could still be possible.