Jo Ann Schiefelbein wrote:

So texture and temperature does not matter in the recipe?

About 45 seconds. Safety isn't an issue.

Pastorio

Here's what I addressed:
After mixing Tablespoon of Vinegar with milk to equal 1 cup...how
long should it "sit" at room temperature to become sour/buttermilk and
safe before using it for baking and etc.?

I have no idea what recipe you're making. When you used the word
"safe," I assumed you were asking about food safety.

Acid curdling to make sour milk is a very quick process.

Pastorio