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There's no need at all to apologize for asking questions, especially when you've clearly done some experimenting and reading on your own before reaching out!

In a script like so:

on click do
 sleep[5*60]
 play["sosumi"]
end

Decker will wait five seconds before playing the sound. If you reverse the order of those operations:

on click do
 play["sosumi"]
 sleep[5*60]
end

The sound will begin to play immediately, with its playback overlapping the 5-second sleep.

You can also use sleep["play"] to ask Decker to sleep until all sound clips have finished play[]ing:

on click do
 play["sosumi"]
 sleep["play"]
end

See All About Sound for more detail and examples.