How long can you drive with faulty oxygen sensor?

Depending on the year of the car, oxygen sensors will generally last anywhere from 30,000, 60,000, to 100,000 miles. Even though they may still function and won't trigger the "check engine" light,...

That depends; for you or for me? I could do one in under a half hour if there are no complications. Probably closer to 15 minutes.

For a short distance ... problem is, with this sensor not working correctly, chances are that your fuel usage will increase dramatically and the engine will not be running at peak performance.

I would say indefinitely. It's not safe for obvious reasons, but your car won't spontaneously explode if it isn't fixed. Depending on the year and type of car you drive, it may throw up a "problem"...

no. the upstream sensor is the one before the catalytic converter and the downstream is the one after