Or if you prefer to compile the timezone data for Israel yourself, it's pretty easy to do (it worked falwlessly for me):

• First, to see your current timezone settings:
  
  Code:

  zdump -v Asia/Jerusalem | grep 2013

  The information is being read from /usr/share/zoneinfo/Asia/Jerusalem.
• Assuming it's incorrect (still showing the switch to IST as occurring in September), download the new data from http://www.iana.org/time-zones, and place it in some temporary directory $TMP, unzip it (note that the contents will be unzipped directly into the current directory, no subdirectory will be created). The new information you need is in the extracted 'asia' file.
• Compile the new information into the format needed by the system (the following has to be done as root):
  
  Code:

  zic -d $TMP_OUT asia

  where 'asia' is the said file containing the new information, and $TMP_OUT is the directory in which the compiled data wil be placed (if $TMP_OUT doesn't exist, it will be created).
  This will create an Asia directory under $TMP_OUT, and inside that directory will be, among others, a 'Jerusalem' file. Replace /usr/share/zoneinfo/Asia/Jerusalem with this new copy (keep a backup of the original, if you want to be safe).
• That's it! issuing 'date' will now show the correct time. In order for the clock to be updated, I rebooted at this point, though I imagine that there's a way to update the clock without a reboot, but I don't know how.

NOTE: Better to compile the new information on the n900 itself. The compiled files on my desktop system are much larger that those on the n900, and when I compiled the new data on my desktop, it, too, produced larger files. Compiling it on the n900 produced files of the same size as the originals.

Hope this helps!
Dov