Lasting time for surges is measured the same way as are sags. Impulse - An impulse is a very short term disturbance up or down superimposed on the AC sine wave that typically lasts between 0.5 and 100 microseconds. In-phase going impulses which increase the instantaneous voltage are called spikes. Spike - An over voltage impulse ranging from 400V to 5600V or more which is superimposed on top of the AC sine wave. These, when over 600V, are potentially very damaging disturbances.
Notches are typically too fast to see.
These typically last as long as spikes but can be up to several milliseconds. In addition, spikes and notches usually come in pairs or in an oscillating series. For every notch there is usually an immediately following spike due to power line inductances and capacitances. All power line disturbances are transient by definition. EMI - Broad spectrum electromagnetic noise interference either conducted on the power line directly from the source or radiated to the power line then conducted to the susceptible equipment.