Headphone break in?

I believe everything in the audio world will benefit from break-in but in your scenario, I don't know from experience how long it will take. I'm sure others don't believe in break-ins and you are entitled to your opinion.

I had purchased a slightly used set of Hifiman HE1000V2 headphones that developed an issue, Hifiman replaced with a new pair under warranty and I have to say it took a good while for them to come on song to the point of me not enjoying them till they burnt in. Enjoy the music

I have found that my headphones, Focal Stelia, Meze Elite, ZMF Verite closed, and others all benefit from break-in time. I usually noticed differences in 25 hour increments with them really settling in around the 200 hour mark. I would leave them plugged in to my amp and run them continuously for a couple of days to help the process. 

It depends; I've had a lot of headphones and some sound really good, if not their best, right out of the box, and others I've gotten that sounded so bad out of the box that I was ready to send them right back, but after letting them break in for about 150-200 hours, they sounded like they were supposed to...