systemd-timesyncd

To set time sync server address on client, you need to edit /etc/systemd/timesyncd.conf:

 # See timesyncd.conf(5) for details.
 
 [Time]
-#NTP=
+NTP=las0
 #FallbackNTP=ntp.ubuntu.com
 #RootDistanceMaxSec=5
 #PollIntervalMinSec=32

$ sudo systemctl restart systemd-timesyncd

Show time sync options:

$ timedatectl show-timesync
SystemNTPServers=las0
FallbackNTPServers=ntp.ubuntu.com
ServerName=las0
ServerAddress=10.225.4.51
RootDistanceMaxUSec=5s
PollIntervalMinUSec=32s
PollIntervalMaxUSec=34min 8s
PollIntervalUSec=34min 8s
Frequency=0

Show timesync status:

$ timedatectl timesync-status
       Server: 10.225.4.51 (las0)
Poll interval: 34min 8s (min: 32s; max 34min 8s)
 Packet count: 0