In my experience 13 days is way too late for steroids to have any realistic chance at preventing permanent damage.
3 days tops. Even then it's not a guarantee. I would take it within the hour, along with NAC supplements to help prevent oxidation and excitotoxicity.
My left ear started ringing January this year out of the blue whilst sitting down watching TV in the evening. It turns out it was likely several episodes of NIHL caused by loud bangs (WH1000XM4 headphones have a hard plastic shell which, when hit hard, really ping crazy loud). No way that they couldn't at least potentially cause damage between 4 kHz and 6 kHz which is where NIHL presents.