wrong time

hi guys, i have a problem with the time on my omv system installed on a rpi 2. The version is 3.0.87.
I set the time manually and the rpi the clock seems maintaining the correct time, but when i turn off the rpi the clock changes totally the time
I tried to use but it does not seem to work. Can someone help me?

ok i find a solution...it is not so beautiful but it is effective...considering that the problem happened at every reboot i solved performing a command during startup...I explain everything to others who have or will have the same problem.

open the file rc.local with the command sudo nano /etc/rc.local
then add before the line "exit 0" the command sudo sntp -s time.google.com
close and save the file and reboot

At each restart the rpi will be forced to change the time using google server