Castiel had explained to him once, what might have been a lifetime ago or at least it feels like it, that time for an angel moves in a different way that it does for humans.
" It's not as linear, I guess," Castiel had told him, frowning lightly as he tried to put whatever he was thinking into words, " it's like it's happening all at once, it's slow but it's also so fast paced it's dizzying if you focus too much on it." Dean had thought back then there must be something wrong with him, because he knew exactly what Cas was talking about. " There are all these fixed points, and all these possibilities too, all these moments that have been, that are, that will be, and those that could have been and won't ever be." Dean could feel a headache starting to form by that point of the explanation. Something must have shown in his expression because Cas had reached out then, pressing warm fingertips to his forehead and vanishing the pain away.
Cas is very much human nowadays, and so is his perception of time, even if sometimes he still talks like he can feel it all in the back of his mind, impossible to grasp, like a missing limb.
" Are you sure you don't want us to do something together to pass the time?" They are together, existing in the same space, but Dean has been doing his own thing for the last half an hour, and Castiel has just been watching him, nestled in Dean's side, head on his shoulder, " Don't want you to get bored or anything." He adds, quietly.
Castiel shakes his head, " we are passing the time together," he shrugs, " it's not so overwhelming anymore, just being, sitting still in one place, letting time pass by." Dean nods along.
" Can't see it all anymore, huh? What is and what could have been, all that jazz."
" No I can't," there is no trace of sadness or regret in his voice, " but I never felt bored back then when I was with you either, just as I don't feel that way now, it was all there for me to feel, even if I could never see or comprehend it fully or clearly, but you already were my favorite moment in time, just as you are now."
Dean doesn't say anything, can't find the words, he quietly goes back to the task in hand, smiling all the while.