Linux – NTP is running, system clock still not in time – what gives

A Debian Stable (5.0.3) server is running ntpd, and connected to the internet. Still, the system clock is about 5 minutes wrong.

$ /etc/init.d/ntp status
NTP server is running..

Relevant parts (I think) of /etc/ntp.conf:

driftfile /var/lib/ntp/ntp.drift

statistics loopstats peerstats clockstats
filegen loopstats file loopstats type day enable
filegen peerstats file peerstats type day enable
filegen clockstats file clockstats type day enable

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

I know NTP doesn't necessarily bring the clock in time immediately. Still, how many hours or days you need to wait in order to reasonably expect that NTP has done its job and synced the clock?

Am I missing some other configuration file or option, or just doing something wrong? Is ntp (instead of e.g. ntpdate) the right tool for this? Is there any quick way to check if configuration is correct and whether the chosen NTP servers return the correct time?

Edit: output of ntpq -p is:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 ns1.nexellent.n .INIT.          16 u    - 1024    0    0.000    0.000   0.000
 dnscache-madrid .INIT.          16 u    - 1024    0    0.000    0.000   0.000
 sinister.wzw.tu .INIT.          16 u    - 1024    0    0.000    0.000   0.000
 dnscache-frankf .INIT.          16 u    - 1024    0    0.000    0.000   0.000

Edit 2: Turns out ntpdate -u 0.europe.pool.ntp.org command (suggested by brent) returns

17 Dec 17:37:29 ntpdate[14195]: no server suitable for synchronization found

…even though on other machines that command works fine. So we'll be looking at network/firewall settings for this particular server (which is in a different network, accessed over VPN).

Resolution: The culprit wasn't local firewall on our server, but firewall settings somewhere in the surrounding network. So we asked the server hosting provider to allow NTP for our machines, and now it works fine. For example, ntpq -p now returns:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 ns1.eunet.fi    192.36.144.23    2 u   10   64    1    1.043    0.258   0.001
 ns2.eunet.fi    62.142.10.44     2 u    9   64    1    0.671    0.135   0.001
 ns3.eunet.fi    62.142.10.44     2 u    8   64    1    0.750    0.277   0.001

(We also switched to eunet.fi servers recommenced by the hosting company, but that is beside the point.) The commands in brent's answer were helpful because they made me realise the problem was in network access to the NTP servers, not in NTP configuration itself. Thanks everyone!