It cannot occur until after he is signed, which cannot occur until after Jordan Mickey is released or Demetrius Jackson is traded. Their contracts fully guarantee on Saturday, so expect one of them to be moved before then, and for Hayward to be signed and introduced shortly thereafter. My guess is Friday, from Vegas.
It's possible that Morris and Baynes will be introduced then as well, but my guess is they'll have a separate press conference in the middle of next week in Boston.