I’d like an option in settings so that when I check off a task, it automatically appears in my calendar at the time I completed it.

I used this exact behavior in another product for several months and found it very useful. It lets me look back at my day and see when I actually finished tasks, almost like a lightweight activity log.

A complementary case: when I check off a task directly in the calendar (when it’s already scheduled to have started), the task then ends and truncates its time slot at the completion time and free up the remaining time in the calendar. It assumes the start time was as set, but adjust the end time. This gives a clearer record of both what I planned and what I actually did, and in effect logs time.

I know some users prefer removing completed tasks from the calendar, which makes sense for them. But having the option to display completed tasks, and even sync them with Google Calendar after the fact as an archive, would make it easier to review past days.

This feature mixes time tracking, task tracking, and the ability to reflect on when tasks are getting done.