How do I make a timer count when the game is off

I am trying to make an idle clicker, that continues to add points after the game is shut off. Any help with the timer would be nice.

Get the system time - https://www.scirra.com/tutorials/940/ho ... -a-project

Convert to base units of seconds.

Record via variable/localstorage/ect.

Compare with last recorded system time on resume to calculate how much time has passed.

This system is cheatable by modifying the system time. Otherwise, you will need a server side time check. Or, figure out how to request the current date/time from a timeserver.

Thanks man, I didn't even know where to begin with this.