I know this setup, it happens before the process time.
Our setup (real world) shall happen every x hours of process time on the station.
I cannot set it as the importer part is disabled/greyed out.
The failure allows me to setup the first start time, any further start time and duration.
If I remember well, your question was :
What is the correct way to implement service/maintenance in the plant simulation ?
The correct way to define set-up in Plant Simulation is to use the set-up features provided
by Plant Simulation.
The Set-up ( in real world) usually depends on the number of produced parts during production
time not solely on a predefined maintenance period.
E.g. welded spots in Body in White production.
From the cycletime ( per part) and your time until setup , you can calculate the part count
input parameter for Set-up in Plant Simulation.
Switch off common resources and you can set the the set-up importer( s.b.)
In any case if you want to use the fixed set-up periods you can always
use the "failure" solution.