The mixture will be very thick and pasty. Do not thin it out! This quick sourdough starter needs that flour for fermentation and energy. You’ll see how thin the mixture gets after 12-24 hours after every feeding.
Look for signs of fermentation: tiny bubbles on the bottom of the starter, pinprick sized bubbles on top. If you don’t see any signs after 24 hours, ensure your starter is being in an area that is at least 75º F.