WaPo reporter says Mueller team is planning on releasing a report on the obstruction part of the investigation in June or July.

More info: Mueller team wants to release report on Obstruction investigation, incidents during President's time in office this June or July. AND THEN they continue with collusion probe. Hot Summer. pic.twitter.com/tFQHd9yZ4y — Josh Marshall (@joshtpm) April 4, 2018

Note that technically, Rod Rosenstein appears to have authorized Mueller to write such a report. In theory, he could decide to keep it confidential. In practice, that seems highly unlikely.