install ntp (network time protocol) server to synchronize time

$ sudo yum install ntp

Now follow this steps:

1. first go to official http://www.pool.ntp.org/en/
2. choose your Continent area where the server physically is located
3. then search for your Country location

For United Sates:

server 0.us.pool.ntp.org
server 1.us.pool.ntp.org
server 2.us.pool.ntp.org
server 3.us.pool.ntp.org

go to ntp config file

$ sudo vi /etc/ntp.conf

Uncomment initials:

#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

copy new United States to config and start

$ sudo systemctl start ntpdate
$ sudo systemctl enable ntpdate
$ sudo systemctl status ntpdate

run this

$ sudo ntpdate us.pool.ntp.org

check the date-time and match it with your cell phones!

$ timedatectl

Local time: Wed 2015-09-09 09:31:09 CDT
Universal time: Wed 2015-09-09 14:31:09 UTC
Timezone: America/Chicago (CDT, -0500)
NTP enabled: no
NTP synchronized: no
RTC in local TZ: no
DST active: yes
Last DST change: DST began at
Sun 2015-03-08 01:59:59 CST
Sun 2015-03-08 03:00:00 CDT
Next DST change: DST ends (the clock jumps one hour backwards) at
Sun 2015-11-01 01:59:59 CDT
Sun 2015-11-01 01:00:00 CST

Since NTP enabled is no above, you can enable it like this (it will ask for your root password)

$ timedatectl set-ntp yes

then check out date-time again

$ timedatectl

Local time: Wed 2015-09-09 09:40:37 CDT
Universal time: Wed 2015-09-09 14:40:37 UTC
Timezone: America/Chicago (CDT, -0500)
NTP enabled: yes
NTP synchronized: yes
RTC in local TZ: no
DST active: yes
Last DST change: DST began at
Sun 2015-03-08 01:59:59 CST
Sun 2015-03-08 03:00:00 CDT
Next DST change: DST ends (the clock jumps one hour backwards) at
Sun 2015-11-01 01:59:59 CDT
Sun 2015-11-01 01:00:00 CST

if you want to restart ntp, then you need to first unrelate ntp from timedatectl

$ timedatectl set-ntp no
$ sudo systemctl restart ntpdate
$ sudo systemctl enable ntpdate
$ sudo ntpdate us.pool.ntp.org
$ timedatectl set-ntp yes

make sure your timezone is also correct
(please follow http://www.putorius.net/2015/04/setting-time-and-date-in-red-hat-7.html to play with timedatectl command)
i.e. list all the timezones just for curiosity

$ timedatectl list-timezones

you can also check the date simply like this

$ date

Wed Sep 9 09:47:35 CDT 2015