Time perception has been shown to be influenced by the attentional guidance from working memory (WM)，with that the stimulus matching the working memory content was judged to last longer than mismatching stimulus. However, the guidance effect might be flexible and modulated by other factors. In this study, we combined change detection task paradigm and time comparison task to exam the influence of ISI (the stimulusinterval between the offset of WM content and the onset of target duration) and target duration on time judgment. Participants were asked to memorize an abstract object (both the color and shape) for a subsequent memory test in which they indicated whether a test object changed. During the delay period, participants had to judge which one of two successive objects was presented longer (or shorter), with one object matched the WM item while the other did not. Mere observation without WM demand was taken as control task to exclude the contribution of repetition. The results showed that when the ISI was short (Experiment 1), time judgment accuracy was greater on memory-matching trials relative to memory-mismatching trials, suggesting the memory-matching stimuli facilitated time perception. However, when the ISI was longer (Experiment 2), the guidance effect declined. On the other hand, irrelevant of short ISI or long ISI, WM task or mere repetition, when the duration to be perceived was longer, matching stimuli inversely decreased perceived time. This study suggests that the effect of visual working memory on time judgment is flexible, and is modulated by the interstimulus interval as well as the target duration to be perceived. The variability of object working memory on timing task might be related to the focus and allocation of attention.