1) Computer creates an array in memory in order to store each player's time.
2) Timer displays seconds as player ponders his turn. (Optionally the display also shows 'player 1' or 'player 2', etc.)
3) As soon as he makes a play, he presses button.
4) Computer adds counted seconds to his total time, stores it in memory.
5) Timer starts counting from zero for next player's turn.
It can get confusing whose time the computer is counting. Each player must push button at end of his turn.