Possible to make sourdough starter quickly?
You aren't going to be able to get a sourdough starter from flour to ready-to-bake in 24 hours. You could easily make a poolish or pâte fermentée in that time, and get some of the flavor. You might also be able to use some yogurt whey or another source of lactic acid to get some of the sour flavor. Unfortunately, a sour starter is something that you kind of need to keep going and have on hand.