I don’t mean what’s the best use of an SWU - I mean how/when do I actually use it to give myself the best chance of it clearing?

I’m an EP with about 300k LPs - I have one SWU left expiring at the end of March and will only have one chance to use it (a JFK-LAX flight I have booked for early March). Is it better to request it now and hope that I get it when and if it opens up? Or to wait until I see availability in the app?

I’ve had horrible experiences in the past when trying to use one when there was definitely space (once I called and the person did not even know what I was talking about, another time it took over an hour while chatting, etc). On the other hand I’ve heard that if I request it before it’s available, it won’t be applied immediately once they open up the space and someone that has an expert flyer alert (or just sees that SWUs are available on the flight) can call and get the spot before me.

Any tips for what would give me the best chance?