In 2370, a T'Lani cruiser was located in orbit of the third planet, and Dr. Bashir and O'Brien were sent there to help the T'Lani and Kelleruns rid themselves of Harvesters, a biological weapon. After completing their task, there was to be a celebration held on T'Lani Prime, thus delaying their expected departure by a day.
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Background information Edit
This planet was only mentioned in dialogue.
According to the script, the pronunciation for T'Lani was " tuh-LA-nee". 
According to Star Trek Encyclopedia (4th ed., vol. 2, p. 356), in the entry for "T'Lani Prime", the system was named T'Lani.