I had a DW contractor mention that method to me once...I remember using a method one of my friends offered. We had a job in downtown to repair Hurricane damage in a tower and had to finish several offices in two days We used about 1/2 regular mud compound mixed with about 1/2 quick set 45 min. and maybe just a tad bit of water. Never actually timed it but it got the job done just took a lttile bit longer to dry and without mixing lots of times and breaking your back. We taped and floated one day and lite skim and primed the painted the next with extra help and staying later to finish. Has anybody tried this?
I don't think there is anything slower to set than 90 minute & 90 is NOT the working time BTW.