Explain-Get accurate real timenode

Can someone explain how “get accurate real time” works. yesterday it was 16778200 an today its 16777700, how yesterdays values can be higher than todays if it get higher every tick??
I need real time for my mobile game, so I can refill action points after some time passed. but when I log in next day, its not replenished because time is lower then yesterdays. Im confused…