How does the speed of institutional response determine whether democracies survive executive power grabs? This paper develops a theory of "structural time lag"—the critical gap between executive action and institutional constraints—to explain variation in democratic outcomes during constitutional crises. While executives deploy emergency powers instantaneously, legislative and judicial checks require procedural timelines spanning hours to months. This temporal asymmetry, combined with constitutional ambiguity, creates windows for democratic subversion through what I term "democratic drift." Using process tracing of recent presidential crises in South Korea (2024), the United States (2021), and Brazil (2023), I demonstrate how response time determines outcomes. Korea's legislature acted within hours but judicial delays enabled prolonged legitimacy contests. The U.S. experienced two months of drift between the election and January 6th, nearly collapsing democracy. Brazil's supreme court intervened within 48 hours, preventing drift through immediate arrests. The findings show that democratic survival depends less on constitutional design than on institutional response speed. This research reveals that democracy's fate is determined not in years, but in hours and days.