I’ve never been an instructor at United, although in a previous life I worked for FlightSafety as a sim instructor on a Hawker. From the time I was hired until I could teach Part 91 guys was 3 months minimum. Then it took almost a year before I was allowed to do Part 91 Checkrides, another 6 months before allowed to teach Part 135 guys.....etc. You get the point. It’s not a quick process to ramp up and qualify a new instructor.