Install chrony:

# yum install -y chrony

Configure chrony to synchronize time with a local ntp server (local stratum 10 is used to serve time even if it is not synchronized to a time source):

# vi /etc/chrony.conf
[...]
#server 0.centos.pool.ntp.org iburst
#server 1.centos.pool.ntp.org iburst
#server 2.centos.pool.ntp.org iburst
#server 3.centos.pool.ntp.org iburst
server ntp.example.local iburst
local stratum 10
[...]

Configure ntp peer:

# vi /etc/chrony.conf
[...]
peer srv1.example.local
[...]

Allow ntp on the firewall (to allow peers to synchronize):

# firewall-cmd --permanent --add-service=ntp
# firewall-cmd --reload
or
# firewall-cmd --permanent --add-port=123/udp
# firewall-cmd --reload

Restart chronyd:

# systemctl restart chronyd

Check:

# chronyc sources
# timedatectl

If timedatectl displays NTP enabled: no, then, enable it manually:

# timedatectl set-ntp true