In biological membranes, it is thought that lipid heterogeneity and lipid domains play a role in membrane functions, such as protein regulation. However, it is difficult to determine the structural and thermodynamic properties of these domains, given the complexity of biologically relevant bilayers. In this study, two phospholipids of different acyl chain lengths, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-diarachidoyl-sn-glycero-3-phosphocholine (DAPC) are combined to create a model system for domain formation. Differential scanning calorimetry (DSC) is used to observe how these domains form over time and to determine whether a stable equilibrium state emerges. Significant changes in the main transition temperature (Tm) suggest that the composition of the bilayer rearranges with time. Furthermore, changes in DSC peak shape and hysteresis between the heating and cooling scans provide evidence that the reversibility of the Tm changes over time.