There will even sometimes daily be incidents where your forensic training comes into play setting you apart and more trusted vs psychiatrists without the training.
But what I think you're referring towards is actually specific work that only forensic psychiatrists are expected to do such as expert witness testimony, depositions, forensic evaluations etc.?
This ranges from hardly ever to daily.
Even most of the top forensic psychiatrists did regular clinical psychiatry. It's not surprising why. You want to keep your clinical skills sharp. E.g. Doug Mossman, a Guttmacher award winner, and churning out publications with high volume, plus being a professor within U of Cincinnati's medical school but also law school, still saw outpatients several days a week.
IMGs earning less? I don't think there's enough of an infrastructure within forensic psychiatry to get a hold of people within the field and show this phenomenon is happening. I do think a court, and lawyers will be more impressed with what the doctor's done in the last 5-10 years instead of where they went to school.
How time consuming? Can be very very consuming. It's also at times hard to work around patients. You could get called in to do expert witness work and given a time and date to appear in court in a manner that just wrecks your schedule. I've had it happen. A colleague of mine in the same office is a forensic psychiatrist and we usually have morning coffee. A few times we've whined to each other that these court things are a pain in the butt. You get called in for court, for example, and you got to drive to court, takes about 30 minutes to just get in there cause all the security, then you wait a few hours, etc.
And yes you bill for the entire thing, but sometimes lawyers refuse to pay you despite that you already had an agreement and they themselves are billing for things like waiting in court, but oh you're a doctor so you don't get to do it but we do....!