The club have issued initial ticket information about the play-offs. It seems very likely that Charlton will be playing at home on Saturday 11th (7.30pm) or Sunday 12th May (12.15pm)
It is also very likely that tickets for the home game will be on restricted sale as probable opponents Portsmouth or Sunderland will sell out the Jimmy Seed Stand.
https://www.cafc.co.uk/news/view/5cc4b6f64d54a/what-you-need-to-know-to-get-your-play-off-tickets