Can speakers sound worse during break-in period?

I purchased a NOS pr of speakers ( I’m not disclosing their name. Not interested in hearing from their haters) and was really liking them before I started to seriously break them in. It seems like after 24 hours they seem to have changed and sound worse, or not as good as they did. Are they just going through changes with some drivers opening up faster than the others? I know there are many components involved in this process and some might be a head of the others. I’m assuming that’s the case and when everything comes together they will sing.
Some things you can’t measure: sweetness, presence, fullness, soundstage dimensionality, brittleness of high frequencies, boomy-ness, thinness, air, wetness, slam, rhythm, wimpy-ness and realism.
I would argue that many,  if not most of those things mentioned also change during break in. Of course,  that may or may not be the intent of your post. 
The answer to your question is YES.  Depending on the speaker they can go through a number of changes during the break in period.
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To find the right position for the speakers and the listening place in your room, to get accustomed to the speakers, to eq the speakers where necessary, that could take a couple of weeks. I guess you can call it break-in period. But if you don't like or have hope for the speakers from the beginning I would say leave them.