Heterogeneous Wireless Cellular Networks (HWCNs) are an essential part of current and future cellular networks as a result of several benefits they offer regarding the ever-increasing user traffic requirement. Network resources are nevertheless limited, and as such, an efficient allocation of resources is vital for the development of the HWCNs. An improvement in the coverage area leads to increased mobile user satisfaction which in turn yields higher revenue for network operators. Minimising power consumption helps reduces CO\(_2\) emissions for economically and environmentally efficient HWCNs. In this paper, by exploiting stochastic geometry, we first analyse the Coverage Probability (CP) of a typical HWCN and evaluate the impacts of propagation model/building types, cell allocation and per-tier power allocation. It is shown that a higher allocation of resources in a more lossy environment generally leads to a higher CP up to a certain threshold. Also, previous research shows that large-scale user behaviour varies over time. To this end, this paper proposes a hybrid Resource Allocation (RA) scheme, namely Time-based RA (TRA), to solve a hybrid optimisation problem of improving coverage area during periods of peak user traffic while minimising total power consumption during off-peak periods. Numerical results show that the proposed scheme achieves up to 25% higher CP during the peak period subject to limited total available power and 57% savings in total power consumption during the period of minimal user traffic given a target coverage probability, when compared to the schemes with equally allocated resources.