This should fix your problem, I have also added a line so that you know the bot has started your timer.

Code:
on *:text:!on:#: {
  if ($nick !isop #) { return }
  else {
    msg # Announcements are starting 
    .timer.timername 0 1500 msg # test 
  }
}

on *:text:!off:#: {
  if ($nick !isop #) { return }
  else { 
    msg # Announcements are stopping
    .timer.timername off 
  }
}


You could also change it from using
Code:
if ($nick !isop #) { return }

to
Code:
if ($nick != YOURNICKHERE) { return }

So it will respond to only your name even if you aren't OP.