It has been shown that the sporadic E configuration observed in the ionograms from equatorial stations can suddenly appear or disappear in a time period of one minute or less. Such short decay (or growth) times are found to agree with theoretical estimates of cross-field instability calculations. These findings further support the identification of Es-q to cross-field instabilities. Attempts should be made to study the real time evolution of these irregularities by backscatter radars or finer time resolved ionosondes.