Poor Man's Timer in Vim

let s:lasttime = reltime()
let g:tick_seconds = 2

function! Tick()
  let l:now = reltime(s:lasttime)
  if l:now[0] > g:tick_seconds
    let s:lasttime = reltime()
    call TickCallback(l:now[0])
  endif
endfunction

function! TickCallback(time)
  echomsg "writing file since " . a:time . " seconds."
endfunction

au CursorHold    *  call Tick()
au CursorHoldI   *  call Tick()
au CursorMoved   *  call Tick()
au CursorMovedI  *  call Tick()