While the Chronology explains timelines in a retrospective manner, examining the finished product, the Keystone Timelines and the Mid-Dimension Timelines must be clarified. Whereas the Keystone Timelines involve all the changes Crono made on his quest between the Lavos Timeline and Keystone T-1, the Mid-Dimension Timelines include the various temporal edits between Keystone T-1 and the Ideal Timeline.
(1.) In this timeline, Lavos has been defeated by Crono and company. The ruined future was sent to the darkness beyond time, and Schala has been absorbed by a relic of Lavos to become the Time Devourer.
(2.) Belthasar somehow becomes aware of Schala's predicament and formulates a plan to free her, namely Project Kid. He organized the construction of Chronopolis and sets the stage for the Time Crash to occur.
(3.) The Time Crash sends Chronopolis through time to 12000 BC, creating a new time-line. The El Nido Archipelago is terraformed and the Records of FATE are constructed.
(4.) Belthasar makes several time warps in the Neo-Epoch to check up on Project Kid's progress and make necessary adjustments to the time-line. This of course would make a new time-line every time he time travels, but only one is shown for simplicity.
(5.) The final results of Belthasar's planning is the birth of Serge and his becoming the Arbiter of the Frozen Flame, Chrono Trigger, Assassin of Time, etc. This occurs in Another World (A). In 1010 AD, when Serge drowns, Schala reaches across time to create Kid in 1004 AD, who will eventually be able to save him. This creates another time-line, Another World (B).
(6.) Kid grows up in in Another World (B) and is not rescued from the orphanage by Serge. He could not do this because he is dead. At some point, Kid travels back in time to 1010 AD and saves Serge from drowning. This action creates a new time-line, Home World (A) and causes the dimensional split. Both the original time-line, Another World (B), and the new time-line, Home World (A) retain their existence.
(7.) The inter-dimensional distortion at Opassa Beach, the "Angelus Errare", allows Serge and company to travel between Home and Another. Traveling from Home World to Another World rewrites Kid's history, creating another timeline, Another World (C).
(8.) Serge travels back in time and rescues Kid's younger self from the burning orphanage. A new time-line is created, Another World (D). When Serge returns to the present (in the new time-line, of course), the past has been changed so that Kid always remembered being rescued by Serge.
(9.) The new Kid growing up in Another World (D) now remembers Serge rescuing her. She eventually time travels to 1010 AD and saves Another World (D)'s Serge from drowning, creating yet another time-line, Home World (B).
(10.) Serge and his companions continue their efforts to rescue Schala, even through they don't know it yet. Again, inter-dimensional travel creates another timeline, Another World (E).
(11.) Schala is freed from the Time Devourer. Another World (E) and Home World (B) are merged, either in 1020 AD or 1010 AD.
Note: If I missed any other instances of time travel, those would produce new time-lines as well.
Only Home World (A)'s Serge is ever playable. Home World (B)'s Serge is subject to Time Bastard.
This clearly shows that there is no causal loop between Kid and Serge's time traveling. The Kid which saves Serge from drowning the first time is not the same version of Kid which Serge rescued from the burning orphanage. It also shows how the events of Chrono Cross did not all occur in one time-line. There were many intermediary steps toward the final goal of saving Schala, and history was rewritten each time.
*** by a point means that a footnote is provided at the end of the timeline. '-' means that an event succeeds everything above it, while a series of '*'s mean that it is unknown which event occurred before the other. '-U-' means that this event is dated according to Ultimania, a flawed guide for Chrono Cross written in Japan that may nonetheless have some credibility. -In the beginning, Chronopolis creates Keystone T-2 by being moved to the past. -Another World (A) - Timeline(s) created by Belthasar's trip back to the modern era to observe Project Kid and make adjustments with the Neo-Epoch. -Another World (B) - Timeline created by Kid's possible introduction in 1004 A.D. -Kid saves Serge after 1020 A.D. in Another World (B), causing the dimensional split and creation of Home World (A). -Serge travels to Another World from Home World (A) in 1020 A.D., rewriting Kid's history and creating Another World (C). -Serge travels back to 1015 A.D. to free Kid's mind from the orphanage incident, creating Another World (D).