In the early days of O2 sensors, manufacturers were concerned about their life and didn't want to get stuck with replacement under the 50K mile emission warranty.

My erstwhile '84 190E 2.3 had a light that the odometer activated at 30K miles to notify the owner that a change was required. If done, the tech removed the bulb from the light. There was no other subsequent change recommended - just the one at 30K miles. When my light came on I removed the bulb. When I sold the car at 49K it still had the original O2 sensor. It ran normally and passed emissions.

The maintenance schedule on my '88 190e 2.6 recommends replacing the O2 sensor at 60K and there is no reminder light like on the '84, but my CA model has some health checks and diagnostics including the O2 sensor. At 75K miles my O2 is original, and it functions properly based on a duty cycle check and scope check of the O2 sensor output about a year ago.

Bottom line is tha O2 sensors are getting more reliable, and there is no need to change them at an arbitrary mileage. You can wait until you get an O2 sensor fault code if your model has O2 sensor diagnostics, and if your car fails emissions, a check of the duty cycle and O2 sensor output is warranted. If you don't have the knowledge and equipment to check these functions and don't want to pay to have it done (assuming you can find a competent tech who can actually perform these tasks) then you can change the O2 sensor at an arbitrary mileage or if you fail an emission test, but you may be replacing a perfectly good sensor.

Duke