The text of Genesis 1, literally interpreted, clearly includes the stars in the list of things created on day 4, along with the sun and moon. Even older translations like the KJV include "stars" in verse 16. Planets in ancient cosmologies (even up to medieval times) would have usually been considered a subset of "stars".
In verse 1, "the heaven" does not necessarily include stars. In the original ancient Hebrew cosmology it would have referred to the "vault" over the earth (or "ocean of heaven"). Those attempting to apply it to modern cosmology might consider it to be "space". Young Earth Creationists do not have a fixed viewpoint on this as I understand it.
You mention Creation Ministries International (CMI) in comments. CMI takes Genesis days very, very literally. It's basically their defining doctrine. I have not been able to locate a definitive statement from CMI about what day the stars were created, but since Genesis states it very clearly as day 4 I would be utterly astonished if CMI did not agree. "The universe" can exist without stars, so saying "the universe was created on day 1" does not have to mean the stars were also.