Whether patients with schizophrenia are impaired in flexibly regulating attention in accordance with fluctuations in cognitive demand to achieve optimal task performance remains unclear. To address this issue, 47 patients with schizophrenia and 47 matched control participants were recruited to complete a time-based prospective memory task. Every 2-min block before the target time was divided into four 30-s intervals, after which the time check and intraindividual response time variability (IIRTV) across these intervals were calculated. Patients with schizophrenia displayed significantly higher IIRTV across all four time intervals and checked time less frequently during the last 30-s interval relative to control subjects. Moreover, the reduced change in time-checking frequency and IIRTV between the first and the last 30-s intervals was related to poorer time-based prospective memory performance in patients with schizophrenia. Our findings provide initial evidence that an inefficient capacity to dynamically allocate attentional resources during an ongoing task hinders dual-task performance in schizophrenia.