WordNet (r) 3.0 (2006):

clock watcher
    n 1: a worker preoccupied with the arrival of quitting time

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "clock watcher":
   dallier, dawdle, dawdler, diddler, dillydallier, do-nothing,
   dolittle, doodler, eye-servant, faineant, gentleman of leisure,
   goldbrick, goldbricker, goof-off, idler, laggard, lingerer, loafer,
   loiterer, loller, lotus-eater, lounger, lubber, malingerer, mope,
   moper, old soldier, potterer, putterer, shirk, shirker, skulk,
   skulker, slacker, slouch, sloucher, slug, sluggard, soldier,
   stick-in-the-mud, tax dodger, time killer, time waster, trifler,
   truant, waiter on Providence, welsher