Thru-hikers use it for six months at a time. It's safe enough for emergency use for someone with no preexisting thyroid issues.
see https://www.cdc.gov/healthywater/drinking/travel/backcountry...
Water that has been disinfected with iodine is NOT recommended for pregnant women, people with thyroid problems, those with known hypersensitivity to iodine, or continuous use for more than a few weeks at a time.