How often security appreciation/analysis has been carried for required area/site/installation keeping in view prevailing pol-social-eco situation?

The timeline is typically not fixed between two points of analysis.  The time frame has to be fluid as to take into consideration the risks of the particular region in which you operate.  For example - a certain type of attack may be more prevalent in a particular geographical area and as such you will tailor your analysis/audits to take place at intervals which provide the best coverage.