A first degree burn would be the immediate reaction
The average flu is about two weeks but the most severe symptoms are in the first 5 days but can subside within 3 days.
The slowest drug absorption/response is definitely oral/digestion route.
The fastest drug response time route would be intravenous, the drugs directly enter the blood so it can work instantly. Snorting/inhaling drug still need time to be absorbed to the blood vessel. It might be fast enough if used for local response (example: asthma). The mechanism probably by mucosa diffusion so its similar to rectal or sublingual route.
