Physical capital takes time to build. Yet, the measurement of time to build and of its response to firm behavior remain scant. We fill this gap using project-level data from India. We document new facts on cross-sectional heterogeneity in time to build; and exploit quasi-experimental variation in credit supply to establish that firms accelerate ongoing projects and start fewer new projects when credit dries up. We rationalize our findings with a novel model of endogenous time to build. A credit crunch increases firm appetite for immediate relative to delayed cash flows. Firms then accelerate projects closer to completion and postpone unbegun projects. Such a mechanism is borne out in the data: projects proxied to be more mature are sped up the most. We quantify our model to match our causal estimates, and the joint distribution of project costs and gestation lags. Endogenous time to build generates endogenous amplification and state-dependence of investment on the distribution of projects along completion stages. Endogenous time to build is policy relevant. Contractionary monetary policy faces headwinds when the distribution of projects skews towards mature projects. Tax policy, in turn, can flexibly reshuffle investment expenditures over time with tax credits.