But thats where I think that people miss. Crono doesn't have to wait before the Porre Elder becomes generous because the Elder was not time traveling, crono was. Now if he was taken into the past with Crono when he gave the jerky to his ancestor, then You would see him gradually change in front of crono. The key I think is that you have to be outside the normal flow of time. Marle was outside the normal flow of time, she didn't belong in 600AD, therefore when the search was called off it took time for her to disappear because her 1000ad self was in the past. Does anybody understand what I'm trying to say?
If the Porre Elder travelled to 600 AD, he would have time traveller immunity.
Did Magus gradually loose his memories or otherwise change in 12,000 AD? He was there for weeks or months, yet at North Cape he recalled the original events of the Ocean Palace disaster. The new version of Janus wasn't even there.
The extra elemental armours do not gradually disappear if they are removed from 1000 AD and 600 AD. That is even the same time-frame as Marle's disappearance.
If something is going to gradually change, what defines the intermediate states?
The existence of paradoxes, like Marle's disappearance, make time travel as seen in the series impossible. Even killing Lavos in 1999 AD, thus eliminating the Day of Lavos record from the future, would be a paradox. Only TTI adequately describes the majority of events in the series.