Best time to write about a scene?

Writers sit in one place and write. They rely on memory for descriptions. But not always. Sometimes, they actually go to the place and write there. One might miss details that would otherwise not be missed, had they gone to the place. Or maybe someone goes somewhere, or sees something. While it is fresh in your mind, it could be helpful to jot down what comes to mind on a piece of the nearest paper.

The reason why I say this is because I was sparring yesterday (Boxing. Muhammad Ali, y'know?) and I noticed things to say, and the feelings, that I normally wouldn't have. Even though I have sparred before.