The first 30-40 minutes are a bunch of mostly trivial or fan-servicey moments from the manga that were left out of the anime adaptation. But the rest is really important characterization and history for Yotsuba that make a really significant difference in how and why the events in the main series play out the way they do (i.e. who Fuutarou chooses). It would be much nicer to view them chronologically - but you'll have to go to the manga for that.
Only the last 20 min are important
The first 30-40 minutes are a bunch of mostly trivial or fan-servicey moments from the manga that were left out of the anime adaptation. But the rest is really important characterization and history for Yotsuba that make a really significant difference in how and why the events in the main series play out the way they do (i.e. who Fuutarou chooses). It would be much nicer to view them chronologically - but you'll have to go to the manga for that.
Most of it can be skipped, bu