I was GOING to return these because I had the same problem. But I heard mixed reviews on the comfort of these headphones so I just crossed my fingers and kept them.
It's not going to get better after 24 hours or a week. I have had these for about a month already and the only way the comfort gets better is if you bend the headphones so that they align perfectly with the shape of your head and ears. After about 2 weeks the comfort was still the same (the pads did get softer) and I was going to return these. But I was like...no way, there's no way that the comfort can be THIS bad. I own a pair of DT770s and between wearing those and these, the DT770s blow these out of the water. But that was before I adjusted the headband and angle of the ear cups. After I did that, I can confidently say that the M80s are A LOT MORE comfortable than when I first got them and I can wear them for nearly 8 hours.
I have done a test run on the comfort of these headphones now - Come home, put them out my ears and literally just sit there with them on my ears for as long as possible before I feel pain in my ears. If I start to feel pain then I just keep readjusting the headband / ear cups. This takes patience...don't give up on the M80s yet I'm glad I didn't.
Kinda sad that they didn't include an audio splitter...but it's only a minor problem.