The 26th century time pod was a small craft used by 26th century historians for field observation.
One of these vessels was stolen by Berlinghoff Rasmussen in the 22nd century who took it to the 24th century and posed as historian from the future. While in the future he attempted to steal several objects from the USS Enterprise-D. He was caught by the crew of the Enterprise and trapped in the 2368 after the time pod returned to the 22nd century. (TNG: "A Matter of Time")
Now back in the 22nd century, Section 31 was able to retrieve the pod for themselves. Over the next two centuries they would attempt to strip the temporal displacement drive from the ship and adapt it to Starfleet systems. In 2377, the drive was destroyed, along with the USS Grolier from a Borg attack. (Star Trek: Phoenix-X: "Displacement Syndrome")
In an alternate reality, in 2377, the drive was installed aboard the Delta Flyer before returning to the primary reality. In 2382, the Temporal drive was installed onto the USS Phoenix-X for a mission to travel to the future. Shortly after the mission, the drive was uninstalled and returned to Section 31. (Star Trek: Phoenix-X: "Temporal Doom! Part I" & "Displacement Syndrome")