Do you mean how long to become Chief Justice? There’s no time limit on that. John Roberts became Chief Justice when he became a Supreme Court Justice. He had not been an associate justice prior to that time.
According to Cspan, Gorsuch is nominated as a associate Justice on Supreme Court. I saw it this morning.
The President appoints a Chief Justice. It's not a seniority matter and there is no requirement that the Chief Justice be selected from one of the sitting Associate Justices.