NTP daemons don't want to do a sudden massive jump in system time. For one, it borks the chronology of entries in your log files, system daemons might freak out, etc. What it does instead is "drift" your system clock into place. If you want to check how far off from "the actual time" you are you can query an ntp server:
ntpdate -q pool.ntp.org
NTP works by adjusting the length of a second on your system by a slight bit so that you slowly get the correct time. It can take a while for the drift to happen if your offset is high. What you can do though is force a hard sync once:
service ntp stop
service ntp start
Sometimes internet routers have problems passing through NTP traffic. The reason is that UDP is a bit more trickier to forward than TCP and sometimes the port is even used on the device itself for an NTP daemon.
To stop ntpd:
To prevent it from starting at boot: