I could have sworn I read somewhere that you should not leave the cans running the entire time.
I wasnt able to find one. I was able to find this:
Draw your own conclusions.
Yeah, don't waste your time because burn-in is a myth. Your ears and brain adapt but parts don't change. If they did, why does burn-in always result in better sound? The law of averages says at least some of the time the sound would get worse.
That is not a proper understand of the law of averages.
For instance, let's say that an out of shape person decides to jog 2 miles a day for a month. At the end of the month, that person will have more cardiovascular endurance. Exercise leads to greater endurance.
Whether or not burn-in works is another point entirely. But you cannot say that it is a myth simply because burn-in doesn't make some headphones worse.
Do we really need to go through all this again?
As you can see here, the properties of this kind of system really do change over time—more rapidly at first, less as time goes on. InnerFidelity had an article on this (referenced in an above post), showing the effect for headphones, the Q701 (do note that the listening test is pretty much a garbage invalid comparison that does not demonstrate what is claimed, so it is not evidence one way or the other). There is a very small change in the response and distortion characteristics.
The effect of headphone placement on the head, pads wearing over time, etc. may be significantly greater.
The effect of people getting used to a headphone's sound is probably even greater than all of the above.
It doesn't seem like peoples' actual claims of break-in effects are substantiated by any of the evidence, because they claim differences much larger than seem to be apparent, types of differences that probably do not occur. As pointed out, it is suspicious that the majority of reports indicate that headphones sound better rather than worse, but this does not by itself rule out the possibility that there is a real (and perceived as positive) change. It's all the other evidence. That said, loosening the mechanical damping by breaking in the elastic materials may have an effect not that different than increasing electrical damping factor, which in theory should be generally positive for most headphones—though any changes are realistically probably still in the "hardly different at all" or "can't tell a difference" ranges.
As for the OP's scenario, break in however you want, as long as you want (0 hours is an option), whatever floats your boat. Just don't use deafeningly loud levels, like above or close to the max power input handling specified by the manufacturer. If it's some reasonable-quality headphone and the level is high enough such that you can stand to keep it on your head, it should be okay.
First things first:
1) I do believe sound changes after some use, especially in the bass departament.
2) I do agree that most of the effects of burn-in are mostly psychological.
In speakers, though, change is more noticeable, but here we are talking about the tiny drivers of headphones.
For peace-of-mind's sake I DO break-in (burn-in, whatever) my headphones. What I do is let the following track list repeat for some hours:
1) 10 seconds 10-20khz sweep.
2) 10 seconds 20-200hz sweep.
3) 50 seconds of heavy drums.
4) 60 seconds of pink noise.
5) 60 seconds of digital silence.
6) 60 seconds of white noise.
The digital silence is intended to give the drivers some rest.
If you follow my procedure, you'll acheive a 23.4% - 24.752% improvement in your overall sound (patent pending).
Naaaah just kidding. Add some brown noise to my list if you want. Or start the sweep from 0hz, I'm sure that'll give you a 0.01% improvement in the same ammount of time. Just kidding again, go ahead and have a blast with burn in, just don't pump up the volume so much.