Just to throw in one more option:
Code
alias mytimer {
  set -e %myvariable 1
  .timermytimer -o 0 1 myfilter
}

alias -l myfilter {
  filter -fkr $+(%myvariable,-,$calc(11+%myvariable)) mymessages.txt myalias
  if ($filtered) inc %myvariable 12
  else {
    unset %myvariable
    .timermytimer off
    write -c mymessages.txt
    echo -a Done!
  }
}

alias -l myalias {
  echo -s Here's the whole line: $1
}

/mytimer starts a timer that spits out 12 lines at a time, and clears the file after there's no more lines left.

If you stop it early and start again, it will repeat the same lines.