Dan has spent the last half hour sitting by himself in the HOH, and then suddenly was called to the diary room. He threw on a headband and bolted out the door. Right that moment an outside lockdown was called for the rest of them.
It's possible that it's nomination time, but since he spent no time acting like he was contemplating his choices, I'm wondering if he's headed to the beach.
BTW, some sites are speculating that Dan is going to the jury house for a visit, and that his overheard comment about Michelle is that he wants to focus his pleading on her. If that's true, they better show us lots of footage. Either way, it does explain the "bury the hatchet" message in the competition.