De meest recente MySQL-rijen selecteren op MAX(time) WHERE time <=x

je kunt het doen met subquery :

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

of gewoon :

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