Is TimeShift on gog fully updated?
Depends what you mean.
As far as I know the last official patch for the game took it up to version 1.2
However the GOG release is 1.02, though it is a "re-release" so they may have started again with the numbering.
Are you asking does the game work on modern systems?
Well it still has the problem with hyperthreaded processors (Intel i3 and i7's) so will still crash if that is enabled. GOG support offered no fix for this other than disabling hyperthreading.
Are you asking if the game is updated like a remaster e.g Modern Warfare, better graphics etc?
This I can't answer at the moment. But as I have nothing to do today I was planning to finally disable my hyperthreading and get my Timeshift on to finally finish this game, so I might be able to answer later. From the screen shots it looks graphically the same, on par with Singularity (awesome game) so a 2010 release.