It varies for us depending on the current number of bf's she has, and relationships she is having with them.
Right now, my wife and I are in a poly relationship with her current bf. So, he has been living with us for about 6 months and fucking my wife everyday. Often, multiple times a day, because he's only 29 yrs old, lol. Plus, he has a thick, 9" cock, and she wants it in her all the time. But, there have been periods where my wife was without a bf for a few months.
When I was in the military, we moved a lot. That usually meant saying goodbye to her current bf, or bf's, and starting over at our new location.