45-60hrs a week typically. Depending on call, you may or may not have more hours on a regular basis. On paper (to a med student) the job may look pretty easy, but I would exercise caution when comparing to derm. 60 hours of inpatient psych becomes mentally taxing. I find the degree of fatigue proportional to the number of personality-disorder/100th suicide attempt on neurontin/chronic re-hospitalization type admits. In that sense, you work with one of the sickest or most debilatated populations. As a student I thought it was the first-episode manic that was really sick but it turns out he's the easiest guy to treat on the floor!
We also don't break up our time as interns between interviewing, doing procedures, operating, etc. It is interview --> H/Ps, daily follow-ups, and more H/Ps. You will rapidly become a skilled psych-intake machine based on raw repetition. To that end, I think it is stressful and can become mundane work. Do we have folks regularly coding or seizing suddenly and severely d/t to hyponatremia? Nope.
I would say expect to work fairly hard in residency. If you do not -- you will suffer later in your career. That said, we have plenty of time to spend with family, exercise, read up, and "live life". I think the fun of psychiatry lies in treating the newer symptomatology and psychosis, but that is because I don't have the nuanced skillset yet to handle patients with 30 years of venturing through hell and back through every diagnosis, drug, and demon under the son. Someday!
Hope this helps.