att.duration.w3c provides attributes for recording normalized temporal durations. [3.5.4 Dates and Times 13.3.6 Dates and Times]
Moduletei — The TEI Infrastructure
Membersatt.duration [att.timed [annotationBlock binaryObject gap incident kinesic media pause u vocal writing] date recording time]
dur(duration) indicates the length of this element in time.
Status Optional
Datatype teidata.duration.w3c

If both when and dur are specified, the values should be interpreted as indicating a span of time by its starting time (or date) and duration. In order to represent a time range by a duration and its ending time the when-iso attribute must be used.

In providing a ‘regularized’ form, no claim is made that the form in the source text is incorrect; the regularized form is simply that chosen as the main form for purposes of unifying variant forms under a single heading.