Urine starts to smell after a week or two when the bacteria begins to set in . As the urine dries it leaves behind urine salts and that keeps it wet for months allowing time for the bacteria to grow in your carpet, it will even pull the moisture from the air to the spot in the carpet keeping it wet longer. If you flush the spot with white vinegar it will get rid of all the urine salts in the carpet . This is because white vinegar has a PH balance somewhere between 3 to 5 and the acid in the white vinegar will break down the urin salts allowing the carpet to dry the next day. Then the carpet will not smell because bacteria did not have enough time to grow in your carpet.
1 You will need a shop vacuum, a spray bottle, a towel, and some white vinegar. 2 Retrieve as much as you can with the shop vacuum. 3 Blot with a towel. 4 Put 1/4 white vinegar and the rest water in the spray bottle. 5 Spray the urine spot and vacuum. Spray and vacuum until it is all gone. 6 Blot with a towel and set a fan to dry.