Before the rest of the series besides the pilot episode.
Timmy's clones appear again on Unwish Island, where Timmy uses them to please the restless creatures/people that he wished away. The inhabitants of Unwish Island use the Timmy clones as servants, volleyballs and drums at their beach club.
Mrs. Turner strangely has her own bedroom and bed in this short.
This is the first episode with an animated title card.
This is the first episode where Timmy has light brown hair.
This is the first time that Timmy is shown floating.
When this was shown as an episode of The Fairly OddParents!, when four of the clones sing "Sweet Adeline" to Vicky as a barbershop quartet, the voice clip of them singing was sped up.
This is the first episode to feature a character having clones of themselves. The second will be in "Escape from Unwish Island!", where Timmy's clones return (See Reference Fact #1) and the third in "Tons of Timmys."