Unfortunately no, the system time is used to calculate Unix time. Unix time is good so you don't have to worry about things like time zones, different numbers of days per month, or leap years.
To get a device independent time, you'll need to connect to an online service or server with a time API. Sorry can't help with that.
There are some tricks you can utilize to limit cheating like a limit to how many days worth of rewards can be stored at a time, and also the inability to go "back" in time. For example, you can lock out the user or freeze the rewards if the day counter is ever less than whatever was last recorded or claimed. You can also do things like have the reward only apply from that day forward. This would require the user to keep their device with they the wrong day/time, which I think most people would not want to do.
In the end, the best advice in my opinion is not to worry about cheaters too much when designing your game. Very few people cheat to begin with, and those that do so get enjoyment from it. As long as it's not detrimental to the rest of your users, just let them have fun their own way. You could spend the effort to design your game to be more fun to begin with to disincentivise cheating instead.
TLDR If the game is online/interactive, you have the ability to check the correct time. If it's not, it doesn't really matter if the user cheats or not.