Make sure you paste this in a script file that does not have a on join event.
I added a . in front of the timer command so you dont have to have added timer started timer halted msgs.
changed the msg #bitefight.mx to msg # cause you already told mirc the channel you wish to check for and send to in the on join. so # is all that is needed there.
I have tested this code and it works on every server I gone on. so hope this helps you.

on *:JOIN:#bitefight.mx: { 
  if ($nick == alejop) { 
    .timer 1 3 msg # Hola $nick , la persona que buscas no esta
} }