This study characterizes student procrastination habits and investigates associations between these habits and student performance on graded course components, student beliefs about their own procrastination behavior, and gender. The procrastination habits of calculus-based introductory physics students are measured via the amount of time before the assignment deadline or "completion time" that students submit their work on relatively short (>30 min) weekly online assignments. With the aid of latent profile analysis, we find that one can meaningfully categorize students into 4 completion time classes that clearly distinguish students between their mean completion time, their week-to-week completion time patterns, assignment completion rates, mean course grades, and proportion of women. Consistent with many studies in a variety of contexts, we find that procrastinating students tend to have lower course grades. Closer examination reveals that completion time is directly associated with the nonexam component, but its association with the exam component is weaker and completely mediated by the nonexam component grade. This is in contrast to student ACT score, which is strongly associated with exam component but only weakly associated with the nonexam component, and the direct association of ACT with the exam scores is only weakly mediated by nonexam scores. Further, we find that ACT score is at best very weakly correlated with completion time. Regarding gender differences, we found that on average women tended to procrastinate less than men, submitting the assignments on average 8 h earlier than men. Considering previous studies, our findings support the hypothesis that procrastination mediates the gender differences in performance on nonexam components.