It may be 90 days under some coverages and scenarios, but per https://www.medicare.gov/health-drug-plans/medigap/basics/coverage, "What's included in foreign travel emergency care? When you travel outside the U.S., most plans cover emergency health care, with a lifetime limit of $50,000. Plans may:
Cover foreign travel emergency care if it begins during the first 60 days of your trip, and if Medicare doesn't otherwise cover the care.
Pay 80% of the billed charges for certain medically necessary emergency care outside the U.S. after you meet a $250 deductible for the year.
If you have plans E, H, I, and J that are no longer sold, they still cover foreign travel emergency care."