Abstract Clouds adjust their albedo, amount and liquid water path to anthropogenic aerosols, and produce a climate forcing. Such cloud adjustments are complex functions of both environmental conditions and interaction time. However, direct observations of temporal changes in cloud adjustments are limited. Here, we develop a method to show observational evidence of substantial diel changes in cloud adjustments within ship‐tracks. Polluted clouds experiencing extended nighttime exposure exhibit higher increases in cloud fraction while liquid‐water path adjustments follow a non‐monotonic evolution. The higher cloud fraction increase persists through daytime. Such diel variations likely stem from diel changes in solar heating and background cloud precipitation, and are important because nighttime changes persist and affect solar radiation during the day. Accounting for diel variations produces a stronger aerosol forcing, by −0.1∼−0.4Wm−2 ${-}0.1sim -0.4,mathrm{W}{mathrm{m} }^{-2}$. Our approach reveals how the temporal evolution of cloud adjustments can have important implications for aerosol‐cloud interactions.