you just said 4 hours, that is closer to my estimate since it also includes taking it out and putting it back in.Are you a master automotive transmission specialist? Do you really know everything about everything? You sure seem to think you do sometimes.
There are very good, very fast mechanics around. I watched with my own eyes. One guy in the Allison dept. Where I used to work at the Detroit dealer. Bring his personal '96ish 1/2ton Chevy. In the shop after work at 5pm. I was on the afternoon shift till 9pm. He pulled the tranny out of the truck, overhauled it, reinstalled it, and drove home when we closed at 9pm.
I am not saying it can't be done in 45 minutes, but how good of a job and how clean is what I am talking about.
I am not saying I know it all, but I have been around enough to know that a quality job can't be had that fast, unless you are cutting corners, or just fixing what you see is bad, but to do a full rebuild from start to finish in 45 minutes...

) If its not your transmission it will be soon.