Several studies have documented that visual crowding not only occurs in the early stage of visual processing, but also in the late stage. The multi-level research is becoming a common trend in visual crowding. Flanker category effect is vital for in multi-level crowding research, that shows the semantic property of flankers can adjust the intensity of crowding. Recent study related to flanker category effect have used a number recognition task to show that crowding intensity affected where objects are grouped by meaning. Additional, previous research has indicated potential associations between temporal factors and crowding intensity. However, no known research has focused on exploring relationships between the flanker category effect and temporal factors. The aim of this study was to investigate the exposure time for the flanker category effect. The research is based on three experiment studies. Participants were asked to identify the numbers in different crowding conditions. The experimental data suggest that the peak of the flanking category effect occurs at the time window of 100-150 ms after the stimulus appears.