Determination of timescales using characterization methods There are 4 different timescales in material characterization (as classified in the Atkins textbook):
a. Time during which a quantum of radiation or a particle can interact with a molecule.
b. Lifetime of excited state of a molecule.
c. Minimum lifetime species must have to be seen as a distinct species.
d. Total time of experiment in which the species is observed.
Now the question is how to determine each of these? Say I have a certain compound and want to know what is the time of interaction of a photon with the molecule (part a). Is there an experimental method or instrument to determine these timescales?
The absorption of a photon en route to an electronically excited Franck-Condon state typically typically proceeds in the femtosecond range.

The lifetime of an electronically excited singlet state mostly is in the range of several nanoseconds. In some cases, however, fluorescence lifetimes in the range of several tenth of nanoseconds have been observed.

In cases where the initial excited singlet state undergoes intersystem crossing to a triplet state, much longer phosphorescence lifetimes (seconds range) are observed.

In order to detect a transient, its lifetime must be longer than the laser pulse needed to generate it. 

Once you've populated a state, you may either use 


time-resolved absorption spectroscopy to record it's spectrum and the decay of the absorption at a particular wavelength over time or
use time-resolved emission spectroscopy to measure the decrease of fluorescence (or phosphorescence emission) intensity at a particular wavelength over time.