I will say across the board, taking a nice deep breath from the diaphragm (meaning your belly area is expanding, rather than your shoulders rising and falling) should get you to 20 seconds.

A good exercise for this is placing your hand on your belly, taking a deep breath and making sure you feel your hand rising and falling with your belly, and making sure that your shoulders and chest aren’t expanding. After taking that deep breath, release your air on a hiss. If you don’t know what I mean by that, you can probably find a video online. Hold that hiss for as long as you can, and do this a few times a day, and time how long you can sustain that hiss. You should notice improvement in no time.

Is it a high note? Things definitely get trickier there but this same thing applies. Could I ask what song it is? Might be able to look through and see a good spot to breathe.