Here is how I do it:
Upon starting the game:
1- I get the server time as a timestamp and store it in a var like (ST), right after that I get the current device time and store it in another var starting device time (SDT).
2- Now, whenever I want to get the current server time I calculate the delta time using the device timer:
delta = Now(current device time) - SDT
and calculate the current server time like so ST = ST + delta
There is one issue though -that I will explain how to solve- is if the user changes the device timer, but the user cannot do that -during game play- unless he/she goes to background mode (lost focus), so adding a listener that listens for returning to foreground mode (gained focus) will let you display a loader until you repeat step number 1 which will refresh your vars.
IMHO, I don't think there is another way to solve this, because if there is, KING -the creator of Candy Crush- would have figured it out. In Candy Crush you can cheat when you have no more lives by manipulating your device's clock.