It is correct that all changes in time should change immediately. The problem is that there always has to be someone who remembers what the past used to be so they can correct the changes, otherwise no one would even know the past was changed and the episode would only last five minutes. This happens often on Star Trek (City on the Edge of Forever, Yesterday's Enterprise, the 2009 Star Trek movie, etc.). The Star Trek animated episode Yesteryear theorized that those who visit the past when the changes are made aren't aware of the changes and remember the old past. This seems to be the case on Timeless since they always have to ask if something was changed after they return.
7 months ago