I would be more than Happy to take your word for it on the references......but my CP is from Germany and will be interested in which para of annex 11 refers to two mins plus or minus 30 seconds. ICAO 007 talks about three mins so there is a real danger that some people think it is three m8 s plus or minus 30 seconds.
There's a lot of confusion about the two vs three minute thing. If you are calculating ETOs to the minute, then a change of three (or more) minutes would trigger a compulsory revision. From an ATC perspective, that means 'more than two minutes' as ATC records ETOs and positions ATO in whole minutes. If however your navigation system calculates ETOs to the second, then rounding kicks in as to whether a revised ETO is required to be reported to ATC. Let's say that your original ETO at a waypoint is 0030. You (or your onboard systems) determine that the ETO is now revised to 0032 and 29 seconds. That rounds to 0032 so there is no requirement to advise ATC of the revised ETO. If however your revised ETO is 0032 and 30 seconds, that rounds to 0033, and so must be passed to ATC as a revision. Hope that clears it up.