I was diagnosed in 2002 and here I am in 2025. My M spike and free light chains have increased but it is still MGUS.
I have paid little attention except when it is and was time for blood draws. My previous hematologist, who retired, wanted bloods every 3 months. My current hematologist orders them every six months.
I feel fine and if I had not gone to Mayo for routine care, my MGUS would probably have gone undiagnosed like so many other people. Over the years my ordinary blood tests (cbc, cmp, etc) have all been normal.
Depending on your lab values, you might want frequent blood tests at first for a couple of years but then if you are stable, every six months might be appropriate. There is no recipe that fits everyone.