Yes, 4 hours of any headphone is too long IMO, for the hearing loss risks more than even the discomfort that may occur. But, you can gently bend them outward to exert less pressure if you like. Everybody will be different, including our over-ears - its the nature of the ergonomic business.
The M-100/LP2/LP were originally stood for "long/live play" headphones, however, we really do discourage using headphones for more than 2 hours straight without a break no matter what. Even when I DJ 6-10 hour sets I sometimes take them off fo 10-15 minutes and switch to Faders, mix a few songs with the monitors and cue points only at low volumes.
You only get your hearing once! Did you see my chart I'm working on?
BTW - what volume level are you at? <85dB?
-v