A time barrier was a warp barrier and the barrier between alternate universes like Elysia and the prime universe.
The warp barrier known as time barrier
The Time barrier was a theoretical limit in warp drive technology, which restricted the top speed of warp-powered vessels. The barrier was broken in the 23rd century.
In 2254, when the crew of the USS Enterprise discovered what they thought were survivors from the SS Columbia, which had crashed on Talos IV in 2236, José Tyler noted that the survivors would not believe how fast they could get back to Earth, due to the breaking of the time barrier that had occurred since the Columbia had crashed. For some time after the breakthrough, warp speeds were referred to as time warp factors. (TOS: "The Cage")
Time barrier of Elysia
The small alternate universe known as Elysia was a parallel time continuum that periodically touched the prime universe in the Delta Triangle region. Elysia was described by Devna, as a pocket in the garment of time. The collisions between the two universes produced time warp vortexes in the time barrier between the universes that allowed passage from one side to the other at high warp speed. (TAS: "The Time Trap")