Many citations from Ancestry db's annoyingly save as "residence".
The arrival year in a census citations will save if you've left the boxes checked to save it. Every census you save that has an "arrival" year and box is checked, will create a new "arrival" event in the time line.
You can clean events in a timeline up, after the fact, by moving (linking) the citation link to one event and trashing the rest of the duplicate (or more) events after you're done.
You can't rename a standard format event. For instance, you've saved (linked) a WW1 draft registration record/citation. The system created it as a *residence* event in the time line. In this case you *add an event*, either choose one from the template list, like *Military* or *custom event* which allows you to name it anything you like. Once the event is created in your time line, you move the citation linked in the *residence* event the system created to the new event you created.
Here is a thread that explains how to move citations, there are a couple of ways.http://boards.ancestry.com/topics.ancestry.ancsite/11595.1/m...
Check out the Member Trees board for more chatter about tree tricks.