When possible. I's nt always possible, and that may also depend on where you work. My big sis was a home hospice nurse, and took her lunch breaks pretty regularly. When we worked together in ICU and ER there were times when we never were able to take breaks at all because we could be short-staffed that day or the place was chaos and it was "all hands on deck!" When I became and NP and worked in both a physician's office and taught in our local university, my lunch breaks were regular. Patient safety comes first as always. When you work in a critical care area you are more likely to have late or absent lunches depending on the acuity or emergent situation present that day on your unit.
Meal times/breaks in my hospital, like many others, are generally "willed" into existence. No one will come up to you and tell you to take a break. When you have a lull in tasks that's generally the best time. Sometimes you don't have a lull and need to put your foot down and take at least 10 mins for yourself.