Justice Gorsuch was confirmed on April 7, 2017, he was sworn in on April 10, 2017 and he participated in oral arguments on April 18, 2017. He wrote the majority opinion on the first case that he joined. All documented on records of the Supreme Court.
Kavanaugh has to be present for all the oral arguments in a case before he can participate and vote. Otherwise, there are only 8 voting justices. There should be no problem since it is a few months before oral arguments begin.