Currently the length estimation of mp3 files is done only with one frame, internally we have seen that this is not accurate enough so have extended this analysis window. This greatly improves the accuracy of the reported length, for example it brings the length estimate in the repro project down to 4.153 seconds. This fix will be released in 2023.2.
There will always be a slight amount of uncertainty with mp3 files, this is by design as using the whole file and measuring every frame is relatively intensive. If you need exact length we suggest you swap format, ogg would be good for this use case.