The paper examines global variation between metro systems by exploring why comparable systems have different operating hours. Current research in transportation studies largely disregards this variation, focusing instead on the optimization of individual systems. This paper sets out with a descriptive statistical analysis of metro systems around the world to identify four cases that are similar in most variables yet differ in terms of their operating hours. A subsequent comparison allows to narrow the scope of analysis to a few variables of interest. Noting an absence of overarching causal drivers, the paper draws from key informant interviews conducted with transportation planners associated with these four systems to capture case-specific rationales for certain operating hours. It then juxtaposes these qualitative data with prominent theories of policy-making. These include Multiple Streams Approach, Advocacy Coalition Framework, Punctuated Equilibrium Theory and Narrative Policy Framework. The paper thus assess the extent to which within-case decision-making in transportation practice follows any discernible patterns. The paper concludes with suggestions on how to make sense of global comparisons of urban transportation.