No worries, I can totally be wrong 
So what you ask is basically what I do but not at the time you expect it, that could work too probably. So for example prior to my fix, something like:
[date=2020-12-20 time=15:00:00 timezone=«Europe/Paris»]
Would give these attributes in parsed markdown:
{"date"=>"2020-12-20", "time"=>"15:00:00", "timezone"=>"«Europe/Paris»"}
Which makes the issue obvious.
After my fix we get:
{"date"=>"2020-12-20", "time"=>"15:00:00", "timezone"=>"Europe/Paris"}
I just think I didn’t have all the cases of quotes handled before. Did you try with the second commit I made?