There are numerous other question on this site about "If oxygen production stopped...?" but all of them appear to still have humans around.
This question is different. In my scenario, we may assume that every single living thing on earth has been exterminated instantly. There is absolutely nothing left alive that either produces or consumes Oxygen using biological processes. We may presume that somehow the processes of life simply stop.
I would presume that there will be all sorts of objects remaining on earth that are not alive that will consume oxygen, such as rusting iron from the multitude of abandoned cars, dried-out deceased organisms and left-over refined fuels combusting and other natural non-biological processes.
While the world in which I am interested is not Earth, it is functionally identical to Earth, so Earth may be assumed to be the planet in question.
How long will Earth retain molecular Oxygen in its atmosphere? I am looking for answers that can give a ballpark figure... for approximately how many days/weeks/months/years/centuries/millennia/aeons etcetera will there be detectable levels of oxygen in the atmosphere, i.e. >= 0.5% Oxygen? Answers with an error of up to ±10% will be considered acceptable.
How will the levels of oxygen decline? Will loss of oxygen occur at a constant rate, begin slowly and accelerate, or begin quickly and occur more slowly as time passes?
The purpose of this is to be able to calculate the approximate percentage of oxygen remaining in the atmosphere at any time between the extinction of all life and the point at which the amount of atmospheric oxygen is negligible (i.e. < 0.5%).