Hierarchical ad hoc networks have gained popularity due to the huge number of mobile devices, as well as the social content distribution which is frequently location based. One major issue of hierarchical networks due to mobility is the overlapping of clusters. The issue is often resolved by merging of overlapping clusters. Some efforts propose immediate merging of clusters, while others suggest contention intervals before merging without detailed analysis of the length of such intervals. The literature lacks a thorough study of the efficiency of merging procedures. This paper represents a comprehensive study of the merging procedures. The paper derives an analytical model to compare the merging procedure with and without applying contention intervals. The effect of varying the length of contention intervals on the cluster stability and energy efficiency is also studied. The results show that adopting contention intervals is not recommended. Instead, to achieve the best energy efficiency when two clusters overlap, the clusters should either merge immediately or avoid merging, depending on the characteristics of the scenario. The analytical results are supported with simulations.