Sadly, she has stated that understudies aren’t allowed to announce when they are going on. But you can look to see if Erikia posts vacation days or if Tee says something like “it might be a grool day to enter the lottery” :)
Barrett will be out the first week in September and last I heard Tee was going to be on 9/3, 9/4, and 9/5 with Gianna going on for the weekend but that may have changed. As others have stated, the standbys and understudies are not allowed to post when they’re on but they will post vague things on Twitter and their Instagram stories to give you a little clue and Tee has done this herself in the past, so keep an eye out on her social media.
"Anybody that goes to the theater, I think we’re all misfits, so we ended up on stage or in the audience.” --- Patti LuPone.