To get back to the original question.

For there to be any significance in a short period of time one needs to resolve events that happen in it

The existence of quantum mechanical uncertainty sets lower limits on space and time because to resolve things that happen in smaller spaces and times it higher energies are needed and in the limit the energy will be so high that whatever happens will exit our universe by creating a black hole. this may just as quickly evaporate but science can never be performed with precisions greater than this.

This gives rise to the Planck system of units for details go to

http://en.wikipedia.org/wiki/Planck_unitsThe shortest possible time the Planck time is 10e-44 seconds

This is the time that it takes light to cross the Planck length which is 10e-35 metres or about as many times smaller than a nucleus, as a nucleus is to the universe, ie incredibly tiny.

The energies involved to do this are very many orders of magnitude greater than the highest energy cosmic rays which are themselves much higher than the highest energies that we can reach or are ever likely to reach with accelerators.

This gives the shortest possible times but when we are considering quantum processes it is not possible to know precisely what happens during the transition but we can in effect measure how long it takes to complete the process.

This is again due to the application of the uncertainty principle. Some of the best known quantum processes are those associated with the emission of spectral lines of light as an electron jumps between two energy states in an atom. If you observe this process very carefully for a specific transition at a very low temperature and pressure it is possible to see that there is a slight variation in the frequency of light emitted and the spectrum line has an absolute lower limit of bandwidth. This can be related to the transition time in the process of emission. Quick transitions produce broad spectrum lines and slow transitions produce narrow ones. This is why the spectrum lines chosen for frequency standards are very carefully selected to be very narrow and precise spectum lines.