Setting time from router

In some older versions, NTP was unwilling to make a big change in the time. In those old days, I used to run "rdate" to a known good time server right after boot to get an initial setting. Today, you can do that when starting ntpd, by using the -g option (perhaps in combination with -q if you want to run just once, not keep it running as a daemon).
But to answer: same way as you'd set the time from any other NTP server, see the responses above. You could substitute for your routers IP address in the example from Phishfry .

Of course, this is also assuming that your router actually provides NTP functionality.
I noticed that /etc/ntp.conf already includes a pool with this line:
pool iburst
So the option flags are all that is needed for a oneshot.
ntpd -gq
How do I set the time on my RPi2 from my router?
This is pretty broad "my router"

Assuming you are using pfSense (since I have helped you over there) And you are running an ntp server on pfSense.
You would need to comment-out pool and add your pfSense address for the ntp server.