Create an Action with an output of type Duration.  I pass in the name of a system property that holds the number of milliseconds I want to set the duration to, then I output this duration to Wait for a Duration of Time flow logic

// can't use sleep because it ties up threads and causes flows to back up, so use this with Wait for a Duration of Time flow logic

var waitFor = parseInt(gs.getProperty(inputs.in_sysProperty));
outputs.out_dur = new GlideDuration(waitFor);