When is audioclip length available ?

I currently load and play audioclips through a coroutine :

 IEnumerator loadSoundClip(string fileName)
     {
         string filePath = Application.streamingAssetsPath + "/Audio/" + fileName + ".wav";
 
         // Start a download of the given URL
         WWW request = new WWW("file://" + filePath);
 
         // Wait for download to complete
         yield return request;
 
         theAudioClip = request.GetAudioClip(false, false);
         theAudioSource = AddAudio(theAudioClip, false, true, 1);
         theAudioClipLength = theAudioClip.length;
 
         theAudioSource.Play();
 
     }

But when I do this :

 StartCoroutine(loadSoundClip("mySoundClip"));
     Debug.Log(theAudioClipLength);

The debug log always returns 0. I suspect this has to do with the update/start/frame mechanism and that I need to wait at least one frame before the variable theAudioClipLength to be populated, before I can retrieve a meaningfull value.

So when trying the following :

 StartCoroutine(loadSoundClip("mySoundClip"));
     yield return new WaitForSeconds(0.1f);
     Debug.Log(theAudioClipLength);

the above works for 90% of the time, but in a few instances, even the 0.1 second delay is not enough.

I can increase the wait time some more, but this seems like a clunky way to go about.
Is there a preffered way to achieve what I am trying to do ?

A related question : is it recommend to also destroy the audiosource when it has finished playing ?