How do students form perceptions of their professors' political ideology? Previous research has shown that students tend to project their own ideology onto professors whom they like, but the opposite ideology onto professors whom they dislike. We build on this research by running a similar survey at multiple points throughout the same semester to see if, and to what extent, students' perceptions of their professors' ideology change over time. We find that the interaction between student ideology and professor favorability manifests early in the semester for students who like their professor, while students who dislike their professor take half a semester or more to project the opposite ideology onto their professor.