The share of immune checkpoint inhibitors (ICIs) used in cancer treatment has rapidly increased in recent years. Although ICIs have the potential to provide a durable survival benefit in a subset of patients, many patients do not respond to these costly and often toxic therapies.Recent retrospective clinical data indicate that the time of day of ICI infusion may be a powerful modulator of their efficacy. These observational studies suggest an enhanced efficacy of morning over evening infusion. However, randomized trials have not confirmed in other fields findings obtained by observational studies, possibly because of selection bias and residual confounding factors. Thus, while the data are intriguing, the time dependence of the efficacy of immunotherapy needs to be confirmed in pragmatic randomized clinical trials. Here, we provide an overview of the modulation of ICI efficacy by the timing of immunotherapy infusion and critically discuss the biological rationale for chrono-immunotherapy, the circadian regulation of the immune system, and the need for pragmatic randomized clinical trials to confirm an effect of the timing of immunotherapy infusions on patient outcomes.