3 days, 5 hours and 12 minutes.
Thats how long it had been since he sent arthur into that lake, since he had died. Merlin didn't think he had moved from that spot since, staring out into the lake, like it would make him come back.

He was vaguely aware that he needed to start moving soon, or else he'd starve to death out here, if he didn't die of thirst, or exposure or what ever else out in these woods. God, he'd have to tell Gwen, and the rest of the knights too. Tell them Arthur, the king, their best friend, was dead. He'd tell them how he tried his best to keep him alive, he did what he could, and he'd see that look on Gaius' face, the same look he gave Merlin when Mordred ran off to join Morgana. The 'Yes this is cruel, but by God, what did you expect.'

He could just not go back, stay here until the moss grew into his skin, the beetles found home in his flesh and the tree roots knotted above him. Stay until the earth fused with his skin and he was unable to leave Arthur, keeping watch forevermore. Death seemed so comforting.

But Gwen needed him, and so did the knights, so at long last he began the long journey home.