This is the issue.
http://www.chronocompendium.com/Forums/viewtopic.php?t=1291&start=30We are assuming in that thread that the moment Marle steps back in time, history reflows to 1000 A.D. complete with the disastrous effect she's had on the world.
But do time travelers operate in their own Time Error? Consider this. Before facing Lavos, Crono bids farewell to Doan, and notes that he will go fight Lavos. Doan notes that it is 9:30 AM. Now, Crono goes back in time, and the presence of his light cone causes the future to be discarded. However, the change is presently so miniscule that for all intents and purposes, the ruined future is completely the same. Except for extremely, extremely slight abberations here and there, the ruined future is almost completely identical to its former counterpart. Now, in 1999 A.D., Crono takes 30 minutes to defeat Lavos; he succeeds, causing the ruined future to disappear and the happy future to exist.
But would the happy future come in as soon as Crono departed to 1999 A.D., or would it come in right when the time was 10:00 AM to Doan? That is, from the reference of points of time on a timeline, it is reasonable to assume that changes to the timeline are incurred on a system of Time Error?
As GrayLensman explained, even the very presence of a person in history will disturb the world subatomically at the very least, causing a new timeline to happen -- I'm not arguing against this. But from the scope of a person timing Crono's actions in the past, would the ruined future exist for 30 more minutes after his departure and THEN be cast to the Darkness Beyond Time upon Lavos's defeat? What are the ramafications of this on the Marle Paradox and the thread above (Telepod Paradox)?
If this is true, then history at the Fair would have started changing according to Marle's personal timeline in 600 A.D. There would probably be about 30 seconds of only slight, subatomic changes from her light-cone as she wondered where she was. The changes would then increase (exponentially?) as a search party found her after 30 seconds. Would this effectively give Crono a grace period to enter the Gate with Time Error and Marle's personal time as a time traveler considered?
If I am completely wrong, let me know. I don't think this is that crackpot "Temporal Inertia" theory, but please, I need more input, especially from the heavy hitter analysts here.