International regimes are composite historical constructions. They are built-up through bricolage, as resource-strapped officials combine operational capacities, frequently turning to outside assistance. Who wins and loses-and why-when organisations are added or subtracted? What happens when inter-organisational relations are recalibrated? Why do regimes cohere as they do? By comparing the development of financial-regulatory regimes and probing other illustrative cases, I offer an explanatory framework that emphasizes the importance of timing and sequencing in determining outcomes. Thinking beyond interstate network effects and switching costs, I distil new data and theoretical insights into how and why temporality matters in global politics. I find that time structures the strategic bargaining contexts that mediate the intense distributional struggles between organisations driving key institutional reforms. The explanatory power of this framework upsets conventional wisdom whereby the distribution of state power, and the dynamics of interstate bargaining, are assumed the critical sources of institutional reform.