Ok, on the key-pressed node, near the beginning of your chain of commands, put a Set Timer and 5 seconds, have it run the function of MakeSoundPlay. On the key-released execution line, put a Clear Timer of the function MakeSoundPlay. In the function of MakeSoundPlay, play your sound.
MakeSoundPlay is a function you create. Easiest way is to select your “Play Sound” Node (or place a Node “Play Sound 2D” for example), right-click, “Collapse to function” and name it “MakeSoundPlay” (name doesn’t matter, if you put the same one in every place).
Then hook up “Set Timer by Function Name” to Pressed, fill out the Function name (as “MakeSoundPlay”); and do the same for “Clear Timer by Handle” with Released. Plug the Handle output from “Set Timer” into the input of “Clear Timer”.