The updates for Trainz can take a while, since they are working with some fairly big files.
However, the patches for TS12 should only take an hour or two (at the most, under normal circumstances) to complete. The patch may appear to stall part way through, this is normal.
We do not recommend using the computer whilst updates are installing, so as to ensure that there is no interference.
So as to avoid interference, or complications, we do recommend doing the following

lease clear out the Temp folder on your computer. When you are ready to install the patch, disconnect your internet connection and shut down all programs (including anti-virus and similar). Now run the patch. We recommend that you leave the patch to install overnight, and that you do not use the computer whilst the patch is being installed. You may also want to try installing the patch under Safe Mode in Windows.
However, if a patch is already running, do not cancel it, as this may mean you will need to re-install Trainz again.
Regards