Well it was said that Dragonopolis was pulled from an alternate dimension, yet it also seems that Another World should, by all rights, be itself a discarded timeline. Another world is the timeline that existed before Kid traveled back in time to save Serge. When she did so, Home World should have become the primary timeline and Another World should have been discarded (curiously, where Crono traveled time to save the future, Kid's travels doomed that future). Instead, Another World became a dimension. Thus, Dragonopolis might likewise be seen as both an alternate dimension (like Another World) and a timeline that should be discarded (also like Another World). Or, I suppose, Dragonopolis might have actually been pulled from the DBT itself (if so, that might help to explain why the Time Devourer had access to the Dragon God to absorb in the first place; it was already there, but then it was pulled back out of the DBT, much in the same way as the dead sea).
There is no evidence, mind you, that the Dragonian Dimension has any relationship to a discarded timeline, but we also don't really know the distinction between dimensions and timelines either.
As for time, allow me to elaborate my question a little more.
If time is elastic, then when a force is applied it should return to its original shape. Or in other words, if time is elastic, then anytime a time traveler makes a change to history, time would behave in a manner as to return to its original shape. If time is elastic, then generally time would not be discarded when a change was made (at best we might say a small section of it was altered or discarded, but the whole remains intact).
If time is brittle, however, then when a force is applied to it, time shatters and is entirely discarded, being replaced by a new timeline.
To note, Time Bastard Theory (and to a lesser extent, Time Traveler Immunity) assume that time is brittle, not elastic. Unfortunately, this is the realm of pure theory; nothing in the games give us a good idea of what time itself is like or how it, as a 4 dimensional object, responds to external forces. It is like we are A. Square, from Flatland, trying to comprehend Spaceland.
People assume that time is a strict progression of cause to effect... but actually, from a non-linear, non-subjective viewpoint, it's more like a big ball of wibbly-wobbly.... timey-wimey.... stuff.