The occurrence and timing of emotion-antecedent appraisal checks are difficult to assess. We report an attempt to estimate the time window of the intrinsic pleasantness check using a dual-task probe paradigm. In three experiments, participants viewed negative and positive pictures. Their other task was speeded responding on a probe superimposed on the pictures with different stimulus onset asynchronies (SOAs). Longer probe-reaction times were observed for negative than positive pictures. This effect appeared at SOA 300 or 350 ms, suggesting that the intrinsic pleasantness appraisal check yields a differential behavioral outcome around 300 ms after stimulus onset, and seems to continue unless attention to picture content is inhibited. This paradigm might be successfully used for the mental chronography of appraisal processes.