Real Time Countdown Timer Function With Ticker

I'm playing a game that requires me to keep track of money that is increased by a variable amount (pre-calculated and in a cell) and in a fixed time interval of 51 minutes weather I play it or not so I want to be able to keep track of the progress of the money gain outside of the game.

So, I need to know the macro coding for a real time counter that will increase the total money amount in one cell based on the variable income (declared in another cell) in the 51 minute intervals.

now... I also need excel to keep track of the value increase even if excel is closed (by the difference in time from when excel was closed last).