Integrated access and bachhaul (IAB), introduced in 3GPP Release 16, is expected to be one of the main enablers for dense deployments in mmWave spectrum. The IAB architecture brings in topology changes, which impact network-related aspects, such as ensuring robust routing of traffic and load-balancing. While an IAB network should be transparent to the UE, its topology design may affect the end-user performance. Of particular importance in these first releases, hence, is to determine and evaluate optimal IAB topologies. This paper addresses optimal organisation of IAB nodes by considering a number of inter-connected aspects, including maximum number of hops, path-length, load balancing between the IAB-donors and traffic demand in the access network. In that, we focus on one of the parameters most sensitive to the architectural changes in the network - delay. Our analysis relies on the connectivity graph obtained by considering some practical aspects of sectorised beamforming using real mmWave antenna patterns.