This page is for changing the NTP time back in time 
( -3 months )
1- Check the date/time
...
[root@server1 ~]# systemctl stop ntpd.service
3- change the date ( manually)
[root@server1 ~]# timedatectl set-time '2016-06-01 18:44:30'
[root@server1 ~]# date
Wed 1 Jun 18:44:32 BST 2016
[root@server1 ~]# timedatectl
Local time: Wed 2016-06-01 18:44:36 BST
Universal time: Wed 2016-06-01 17:44:36 UTC
RTC time: Wed 2016-06-01 17:44:37
Time zone: Europe/London (BST, +0100)
NTP enabled: no
NTP synchronized: no
RTC in local TZ: no
DST active: yes
Last DST change: DST began at
Sun 2016-03-27 00:59:59 GMT
Sun 2016-03-27 02:00:00 BST
Next DST change: DST ends (the clock jumps one hour backwards) at
Sun 2016-10-30 01:59:59 BST
Sun 2016-10-30 01:00:00 GMT
...
[root@server1 ~]# systemctl start ntpd.service
...
5- On the client: stop, resync, start and check the date/time again
[root@centos7 ~]# systemctl stop ntpd.service
[root@centos7 ~]# ntpdate server1
1 Jun 18:51:38 ntpdate[30720]: step time server 192.168.0.10 offset -6093937.698513 sec
[root@centos7 ~]# ntpdate server1
1 Jun 18:51:46 ntpdate[30721]: adjust time server 192.168.0.10 offset 0.000031 sec
[root@centos7 ~]# systemctl start ntpd.service
[root@centos7 ~]# ntpstat
synchronised to NTP server (192.168.0.10) at stratum 7
time correct to within 1012 ms
polling server every 64 s
[root@centos7 ~]# ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
*server1.hp8300 LOCAL(0) 6 u 8 64 1 0.310 -0.002 0.006
[root@centos7 ~]# date
Wed 1 Jun 18:52:15 BST 2016
[root@centos7 ~]# timedatectl
Local time: Wed 2016-06-01 18:52:30 BST
Universal time: Wed 2016-06-01 17:52:30 UTC
RTC time: Mon 2017-04-10 17:53:01
Time zone: Europe/London (BST, +0100)
NTP enabled: yes
NTP synchronized: yes
RTC in local TZ: no
DST active: yes
Last DST change: DST began at
Sun 2016-03-27 00:59:59 GMT
Sun 2016-03-27 02:00:00 BST
Next DST change: DST ends (the clock jumps one hour backwards) at
Sun 2016-10-30 01:59:59 BST
Sun 2016-10-30 01:00:00 GMT