There's no reason for him to stay in the first world longer than everyone else since they are all using the same sedative....but we don't know how long they waited to kick or how long they had(because they def didn't seem to be in a hurry when they got back into the first level and swam up to shore).....so I'm not sure why you are saying the sedative would have to wear off between the van hitting the wall and hitting the water.