My advice would be to just use them. Give them a week is what I always say. I personally believe that burn in occurs, but does not provide an absolutely massive difference. The absolutely massive difference is the "brain burn in" that occurs when your brain adjusts to the sound signature of a new headphone.
For a personal example, my first entry into the world of audiophilia was a pair of Beats Studio Wireless. They were overpriced and mid-bass heavy, but they were so much better than anything I had heard before that I was amazed. I used them for several months and joined this forum because I became so intrigued with headphones. Then, after much research, I got the RHA ma750. They were so much clearer than my Beats and I loved the detail, but they had almost unbearably harsh highs. After several months of daily use, the highs seemed to not only settle down, but became my absolutely favorite part about the ma750. But they ended up having a defect (bass went completely to left side for a few days, and then they went back to almost normal) and I had a replacement pair sent to me. I was disappointed that I would have to go through all of that burn in again, but when I gave the new pair a first listen, they sounded extremely similar to my old pair. I was shocked, but then it started to make sense why they seemed to change so dramatically.
Of course, every headphone is different, and sometimes differences even occur between two of the same headphones (my first pair also had a defect, which may have something to do with the differences) so there is no definitive answer as to whether burn in will help a headphone or is merely placebo and headphones won't change that much. Like I said at the beginning, I would just use them for a while and enjoy them.
Of course, this is only the opinion I hold and should not be taken as gospel. As always, YMMV.
