53BP1 acts at the crossroads between DNA repair and p53‐mediated stress response. With its interactors p53 and USP28, it is part of the mitotic surveillance (or mitotic stopwatch) pathway (MSP), a sensor that monitors the duration of cell division, promoting p53‐dependent cell cycle arrest when a critical time threshold is surpassed. Here, we show that Polo‐like kinase 1 (PLK1) activity is essential for the time‐dependent release of 53BP1 from kinetochores. PLK1 inhibition, which leads to 53BP1 persistence at kinetochores, prevents cytosolic 53BP1 association with p53 and results in a blunted MSP. Strikingly, the identification of CENP‐F as the kinetochore docking partner of 53BP1 enabled us to show that measurement of mitotic timing by the MSP does not take place at kinetochores, as perturbing CENP‐F‐53BP1 binding had no measurable impact on the MSP. Taken together, we propose that PLK1 supports the MSP by generating a cytosolic pool of 53BP1 and that an unknown cytosolic mechanism enables the measurement of mitotic duration. Synopsis Following an abnormally extended mitosis, cells activate p53 via 53BP1. Surprisingly, 53BP1 kinetochore localization is dispensable for this process, whereas PLK1 activity, a negative regulator of 53BP1 localization, appears to be essential. 53BP1 kinetochore localization is dispensable for the mitotic surveillance (or mitotic stopwatch) pathway (MSP). PLK1 is required for the MSP. PLK1 activity promotes 53BP1 kinetochore dynamics and 53BP1‐p53 complex formation. Following an abnormally extended mitosis, cells activate p53 via 53BP1. Surprisingly, 53BP1 kinetochore localization is dispensable for this process, whereas PLK1 activity, a negative regulator of 53BP1 localization, appears to be essential.