If the file is correct, then it should work.
Here's the skinny...
(1) The various files in /usr/share/zoneinfo are time-zone information files. (See, e.g. man timezone.) There should be one for every time-zone on the planet, including daylight-savings time.
(2) The ln command creates symbolic links, where one file points to another. The file /etc/localtime should be such a symbolic link, pointing to one of those files.
(3) See man ln for information about the ln command and its options.
(4) Changes to the link should take place fairly immediately. I say "fairly," because programs (like the clock-program on your desktop) load this information from the timezone-file when they start up. They don't re-read it constantly; only when told to do so. So if you change the timezone, you might need to either log-off or to, say, push the button to "change clock options" ... hoping that your desktop-clock will then be prompted to notice the change.
(5) In most cases, the system clock is always set to UTC: Coordinated Universal Time. Thus the binary value in the clock-register does not change; only its interpretation when presenting the time to you.