Niantic previously confirmed Pokémon Go players would be able to complete the “Distracted by Something Shiny” Special Research, and now, players have an exact date that they will need to at least start the Special Research by.
Starting from Feb. 28, players will no longer be able to start the Shiny Celebi Special Research even if they did take part in the Pokémon the Movie: Secrets of the Jungle event. If you have already started the research tasks before this date, though, you can continue grinding through it at your own pace with no worries.
This timeline coincides with Jessie and James spawning in Pokémon Go, as Niantic also extended the amount of time they would be available to encounter in their Meowth balloon beyond the Dec. 17 end date for the event.
If you want to finish the Shiny Celebi Special Research in a timely fashion, you should probably try and get it done before Feb. 28, because if Jessie and James do stop spawning in the game, it will be much harder to get it done. One of the research tasks requires you to beat the Team Rocket duo four times, which will not be possible if they are no longer available to battle.