Lan Wangji didn't realise that he'd gone back in time till he saw the older version of the Cloud Recesses, before the fire. He didn't know how or why it happened but he knew it wasn't the insence burner this time. He and Wei Wuxian were fiddling with some old talismans they found, which were not labelled and neither of them had a clue what they did. All there was with them was a slip that said "works one day, sunrise to sunset" so Lan Wangji just assumed that he'd be stuck in the past for a full day.

He'd managed to arrive in the evening and while walking to the Jingshi, since it was Lan bedtime hours, he'd seen someone hide behind a building after jumping off the roof. He quickly chased after them when his suspicions arose and quickly grabbed the young mans wrist, which wasn't holding a jar of wine.

"Wei Ying.." Lan Wangji stated and Wei Wuxian(you) turned about, about to start his whole spiel about 'it was the last time, please don't tell' when he noticed it too. A taller, stronger, definitely at least 20 year older, version of Lan Wangji before him.