In this article it states that his friend said to Sky News that he went to buy cigarettes:Where did he buy the cigarettes from? I've totally the missed mention of a shop
This article from Sky News states only that he went out to smoke and then came back in and said he wanted to go home: Jay Slater: British teen missing in Tenerife had cut his leg and didn't know where he was, friend says
Either way it does indicate that the people who's apartment he was at were awake when he left.