Can’t cancel purchase

I bought a 37$ item and once I bought it the buyer said “ is it fine if I deliver in a few hours” I said that’s no problem and waited a few hours and never got a response. He messaged me around 12 ish hours later. At that point I was already asleep. I woke up 3 hours later and told him. It’s been 12 hours from than. When can I cancel the order?
If I could get some help that would be greatly appreciated, thanks!
After Delivery time + 12 Hours Grace Period. Can see the article for more Information.