The Darkness Beyond Time is the final wastebasket for timelines nullified by time travel. It can be accessed physically as a place, and served as the home of the Time Devourer. Apparently, when Lavos was defeated, he was relegated to the darkness; there, he took advantage of Schala, who had been transported there by the Ocean Palace Incident. He bound with her to evolve into the Time Devourer, a being that once matured would be capable of consuming space-time. The Dragon God also was sent there somehow after its defeat at the hands of Chronopolis. The Darkness Beyond Time's mechanics are largely theorized, however; it is stated that when timelines are nullified, they end up in the Darkness Beyond Time. In the final battle, tiny, transparent globes of what appeared to be locations passed through Serge and the Time Devourer; these can perhaps be inferred as discarded timelines. In any event, special conditions are needed to access the area. A catastrophic dimensional distortion threw Schala there, while Serge employed a Time Egg and special portal arranged by Belthasar to achieve passage.
Chrono Trigger DS
In the ending "Dream's Epilogue", the party encounters the Dimensional Vortex in 12,000 B.C., 1000 A.D., and 2300 A.D., and completes them by defeating their shades. At the End of Time, Gaspar reveals that his bucket to the Day of Lavos has been overwhelmed with power from the Darkness Beyond Time, representing a new threat. The party enter the bucket and find a version of Magus from a time position after Lavos's defeat; Magus relates that a new enemy has emerged in the Darkness Beyond Time—the Dream Devourer, capable of feeding on thoughts, dreams, and memories across time.
The party follow him through a Gate to the Devourer and find Lavos merged with Schala, who floats in a bubble above the eye of Lavos. Magus tries to defeat the Dream Devourer and free Schala to no avail. Schala reveals that she wants all existence to be destroyed and battles the party, who barely defeats the creature. The Dream Devourer is mostly unaffected, and Schala incapacitates the party. Magus returns, but Schala awakens and tells him that no power can save her, and that he should live his life to the fullest before the Dream Devourer eventually consumes everything. She sends Magus away, then returns to her sleep, and the Dream Devourer presumably continues its evolution to become the Time Devourer.
Please note that in the English translation of the game, the DBT is erroneously translated as "Beyond Time's Eclipse". The original Japanese verifies that this is the Darknses Beyond Time.
Theory and Analysis
Translation: Beyond the Darkness of Time
-The Darkness Beyond Time exists as a repository of discarded timelines of the Keystone Dimension. -The Darkness Beyond Time's timeline runs "perpindicular" to the outside world. -Schala is transported here in the Keystone timelines in the Ocean Palace incident. -The defeated Lavos somehow comes here. -Lavos, even in his defeated and condemned state, is able to fuse Schala onto himself to create the Dream Devourer. -Schala endorses the fusion due to her desire to destroy all existence. -The Dream Devourer begins maturing and feeds on dreams, thoughts, and memories. -Magus finds his way and tries to rescue Schala, but is defeated. -Schala awakens and tells him he can't save her. -Schala sends Magus away and returns to sleep. -The Dream Devourer matures into the Time Devourer, which begins its own maturation process. -The Darkness Beyond Time remains the same for both the Home and Another Dimensions upon the Keystone Dimension's split. -Serge's party arrives here via the Time Egg and possibly the Frozen Flame, and defeats the Time Devourer. -Schala is freed, and Serge's party is returned to the Ideal Timeline.