You will need a button for each different audio sample the user can choose, and one variable that stores the identity of the sample that is currently selected (probably a string var with the name of the sample). Whenever the user presses one of the buttons, you set your variable to the sample name associated with that button (could be the name of the button node). Then when the timer ends, it takes that variable and tells the SamplePlayer to play that audio sample.
How you make the interface usable is up to you. The buttons could be regular buttons, a set of radio buttons, options in a drop-down menu, or something else.
