The following is for a custom window, haven't checked for a dialog yet:
Code:
alias clockStart {
  window -c @Clock
  window -z @Clock
  echo @Clock $asctime(H:nn:ss)
  .timerclock 0 1 //rline @Clock 1 $!asctime(H:nn:ss)
}

alias clockStop {
  timerclock off
  window -c @Clock
}
That works, however, as said, it's in a separate custom window, so I'm not so sure it is all that useful. You can tile your windows to see it all the time smirk Where did you originally want it displayed?