A concurrent program by default gets assigned to Standard manager. So in your case, you have to exclude this particular program from Standard manager list.
If you have a program that can take 18 hours to complete then it seems pointless having a manager with a 12 hour work shift!? What on earth is the program doing that takes 18 hours!?
I will agree with you.
My doubt is ,mentioned program included in Custom Manager, before completion of the program if the work shifts of Manager get completed
In this case what is the situation of running concurrent program.
IF the job is already running on a different manager then no, it should not "shift" to the standard manager mid execution