If you complete any stage when the last two digits of your countdown timer are the same (ex. 177, 233, 088) a bonus mushroom house will appear on the far left side of the world map. Stopping the timer with 11, 22, or 33 will give you a red mushroom house with a random item box. A timer with 44, 55, or 66 will give you a green mushroom house that rewards you with 1-Ups. Stop the timer at 77, 88, or 99 and you'll unlock an orange mushroom house that gives you a Mega Mushroom.