Device Independent Date Time

Hello, I am making a mobile game that allows the player to play offline, and in the game there is a free gift system where player gets a free gift from time to time. So I need to know how many seconds has passed since the player gets a free gift for the system. And I understand that using DateTime.Now would just get the device time so that the player can cheat by setting the device time. Is there anyway to get a device independent time without getting online?

Thanks

 

No, online is the only way.

--Eric

 

Crossy Road seems able to do it. I force quit the game, switch on flight mode, set time become 1 hour later, back to the game and the free gift time still the same!

How the hell!!!

 

I haven't tested Crossy Road and how it works, but maybe if the game isn't played online, the "gift time" stays the same as the time when you closed the game, and updated only when you're online again. This means the "gift time" is only counting down when you're actually playing the game (if you're offline).