Comment 6 for bug 756406

Same issue in 12.04:
$ apt-cache policy indicator-datetime
indicator-datetime:
  Installed: 0.3.94-0ubuntu2
  Candidate: 0.3.94-0ubuntu2
  Version table:
 *** 0.3.94-0ubuntu2 0
        500 http://archive.ubuntu.com/ubuntu/ precise/main i386 Packages
        100 /var/lib/dpkg/status

The only way to add/modify ntp servers (that I can find) is to modify /etc/ntp.conf directly. For example, to change the default ntp servers, I need to edit /etc/ntp.conf directly:

# Use servers from the NTP Pool Project. Approved by Ubuntu Technical Board
# on 2011-02-08 (LP: #104525). See http://www.pool.ntp.org/join.html for
# more information.
# server 0.ubuntu.pool.ntp.org
# server 1.ubuntu.pool.ntp.org
# server 2.ubuntu.pool.ntp.org
# server 3.ubuntu.pool.ntp.org

Change to:

server 0.us.pool.ntp.org
server 1.us.pool.ntp.org
server 2.us.pool.ntp.org
server 3.us.pool.ntp.org

Previously there was an option to change servers from the GUI:
<https://help.ubuntu.com/community/UbuntuTime>
(note: ignore the fact that the page is out of date, I'm only pointing to it to show the previous way ntp servers could be selected/added)

Why would I consider changing from the Ubuntu default?
$ ntpq -p 0.ubuntu.pool.ntp.org
     remote refid st t when poll reach delay offset jitter
==============================================================================
-ns1.your-site.c 108.59.14.130 3 u 147 1024 377 32.085 -5.194 1.320
+vpn.cumquat.nl 193.79.237.14 2 u 202 1024 377 110.477 -0.399 0.653
*ccadmin.cycores 130.207.244.240 2 u 46 1024 377 43.570 -0.138 0.346
+ntp2.ResComp.Be 128.32.206.55 2 u 527 1024 377 67.516 -0.816 0.919

None of those servers are in the US (my location).