The Collaborative International Dictionary of English v.0.48:

Timeserver \Time"serv`er\, n.
   One who adapts his opinions and manners to the times; one who
   obsequiously compiles with the ruling power; -- now used only
   in a bad sense.
   [1913 Webster]

WordNet (r) 3.0 (2006):

timeserver
    n 1: one who conforms to current ways and opinions for personal
         advantage

Moby Thesaurus II by Grady Ward, 1.0:

91 Moby Thesaurus words for "timeserver":
   Benedict Arnold, Brutus, Judas, Judas Iscariot, Quisling,
   Vicar of Bray, apple-polisher, archtraitor, ass-licker,
   backscratcher, backslapper, betrayer, bootlick, bootlicker,
   brown-nose, brownie, careerist, chameleon, clawback, cockatrice,
   conniver, conspirator, conspirer, courtier, creature, cringer,
   double agent, double-crosser, double-dealer, dupe, egotist, fawner,
   flatterer, flunky, footlicker, formalist, fortune hunter, groveler,
   handshaker, helot, hog, individualist, informer, instrument,
   intrigant, intriguer, jackal, kowtower, lackey, led captain,
   lickspit, lickspittle, lone wolf, loner, machinator, mealymouth,
   minion, monopolist, narcissist, peon, plotter, puppet, quisling,
   rat, road hog, schemer, self-advancer, self-pleaser, self-seeker,
   self-server, serf, serpent, slave, snake, spaniel, stooge, suck,
   sycophant, temporizer, timepleaser, toad, toady, tool, traitor,
   treasonist, trimmer, truckler, tufthunter, turncoat, weathercock,
   yes-man