You can see in the first post of the following thread how we will time TSK and TPR campaign missions played in the Steam version (and/or the Original game and/or its patches). Simply put (but please see that post for more details), we multiply RTA by 0.92 to convert the run to KaM in-game time.

https://www.speedrun.com/kam/thread/gdgon

But the following video pretty much sums it up (with an example).