As a student information system who captures student tardiness and other absence events in minutes, I want to avoid complex and error-prone calculations involved in estimating what percentage of time that is for the student's overall day.
We have seen evidence that some SIS systems will capture elements like tardiness in terms of times and duration in minutes. The 3.1 model forces these values to be converted to fractions of a day, which can be complex and result in loss of data.
A better system might capture the "event duration units" and offer 2 possibilities: "school days" or "minutes" (the assessment domain model does this with scores for example).
Also, consider that specific times may be captured as well, as in the "student arrived at 9:25" - while we have not seen it yet, time information could be relevant/helpful for operational use cases ("did the student miss Algebra 1 on Thursday"?)