I spent 2 years at FDX with an extra job as a simulator instructor.
The sim flying didn't count toward FAR time so FDX never cared about how many days/hours I taught in the box.
As far as duty time, if you are legal on the jumpseat you are legal for the trip. If you had some FAR duty time earlier that day in the sim then you are on your own if something goes wrong. How far you want to push that envelope is up to you.