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.