The Best Time to Switch is Now
You cannot simply switch from Medicare Advantage to Medigap any ole time.
The challenge is to avoid a lapse in coverage; otherwise, you will be left with only original Medicare (Part A and Part B). That will leave you exposed to the 20% that Part B doesn’t cover, and the Part A Inpatient Hospital deductibles and copays. This is the key point that I have said in about 1 million places (slight exaggeration, you get the point).
Medigap acceptance should be secured first. Then, and only then, should you feel comfortable in selecting a Part D plan.
Another time window is during the Medicare Advantage Open Enrollment Period, which runs from January 1 – March 31st, 2022.
Carriers will accept your application with varying rules, and this needs to be checked, now, because the sooner that you know the Medigap application result, the better.