Hmm.  411-61=350.  Three seconds difference looks a little odd.  But doesn't explain 60 vs 61 making the difference in the test.

Can you change it back to 60 (or even less) and see what the values look like when the test fails?

It is interesting (and possibly meaningful) that the last modified time 'before' appears to be in the future compared to time.time by 3-plus seconds.  That would at least explain why the test fails without the patch.