CentOS7ではntpdでなくて、chronydで時刻同期します。

systemctl start chronyd && systemctl enable chronyd

# chronyc sources
210 Number of sources = 4
MS Name/IP address         Stratum Poll Reach LastRx Last sample               
===============================================================================
^- ntp03.lagoon.nc               3  10   377   434    +27ms[  +27ms] +/-  140ms
^- y.ns.gin.ntt.net              2  10   377   870  -2303us[-2303us] +/-  106ms
^- time.cloudflare.com           3  10   377   199   -286us[ -286us] +/-   64ms
^* ntp.arupaka.net               2  10   377   20m   +281us[ -698us] +/-   11ms

chronyc -a makestep