What is it?I've heard references to this agency time and again in several Trek books and shows/movies,but none of it has any info regarding the actual agency.
What do they do?Is it just a punitive bureaucracy that slaps the hands of captains who feel the need to hit rewind on the timeline?Is it an actual agency with arrest powers and agents who actively change the timeline?
It's a civilian department in the Federation government with authority over temporal anomalies and incursions. It's the body that regulates the use of time travel technology and temporally dislocated technology.
Dulmer and Lucsley from "Trials and Tribble-ations" in DS9 were part of DTI.
At least one Strange New Worlds
story established that DTI maintains a sophisticated computer network that utilizes chroniton radiation to shield the records from changes in the timeline, with which DTI agents detect time travel and then correct it.
It's not just a bureaucracy for the sake of bureaucracy; it actually does stuff. Whether DTI is its own executive agency within the Federation government, complete with its own Secretary of Temporal Investigations who serves in the Cabinet, or whether it's a division of another Federation executive agency (presumably the Department of Justice) is as yet unestablished in the novels.