Väljer de senaste MySQL-raderna med MAX(tid) WHERE tid <=x

du kan göra det med subquery :

select t.userID, max(t.time)
from
   (
     select userID, time
     from tableName
     where time <= nnn
   ) t
group by t.userID

eller helt enkelt :

     select userID, max(time)
     from tableName
     where time <= nnn
     group by userID