Time it takes for my Jetta's computer to re-register?

I have a 1999 Jetta GL 2.0L A4. My registration recently came up for renewal and in order to get it registered I needed to get my first smog check. I found out this could not be done because the check engine light was on (It had been on for almost a year). The temparature guage had just broke so I relplaced it and had the computer reset thinking that may have been the problem.

After about 300 miles of driving the check engine light came on again. Okay, I go back to the mechanic and he tells me that his Snap-on computer reader show the car is running to rich. So I replace both the O2 sensors, reset computer again and have now been driving on it for 350 miles without the light coming back on.

Now here's the catch. My mechanic told me to wait at least 200 miles before I go and get the smog check because the computer needs to "relearn" my driving habits or whatever. Well I took the car in at

My question...How long does it take for the computer to re-register completely? I have the smog info as well if that might help.

Thanks,

Phil