Can not set past time in ubuntu 16.04

I am trying to set past time Ubuntu 16.04

Here what I did

- First I off the ntp service and then set ntp false using timedateclt the command is

 timedatectl set-net flase

also i disable ntp service using this command

 systemctl disable ntp

After that i set time manual using this command

 timedatectl set-time "11:00:00"

After reboot system, it set the current time but not past time which i set.

Also using this i can set future time but not past time.

For example lets assume right now it is "11:00:00", so i can set "12:00:00" but not "10:00:00".

Please guide me regarding that,am i missing something?

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