Dateless Timelines
You may want to build a timeline for something that has no specific dates.
Preceden does not officially support events without dates, but there is a workaround that gets you most of the way there:
Add Events
Let's say you have two events:
- Product Launch at Time 0 (T0)
- Marketing Campaign at Time 5 (T5)
When you add them to your timeline, make the dates 2000 for T0 and 2005 for T5:

Your timeline will look something like this:

Update the Timeline's Appearance
Next we'll update the timeline's appearance so that it hides the dates.
First, click the Appearance button above your timeline, then open the Content Visibility section and uncheck Dates under Display on Timeline.
In the same section, also uncheck Dates under Display in Popup & Event List. Otherwise the stand-in years still show when someone hovers over an event and in the event list below the timeline.
Then head to the Axis section and uncheck every option under Position.
Click Save Changes when you're done.
Drum Roll...
You'll now have a timeline without dates:

If you want the timeline to show T0, T5, and so on, add them to the event names manually:

Fictional and Invented Calendars
The same workaround is how you build a timeline on a calendar that does not exist, for a novel, a game, or a fantasy setting of your own. Preceden's date fields read real calendar dates, and the month names come from the timeline's language setting, so there is no way to define custom months or rename the years.
Choose real years as stand-ins, in the order and spacing your own calendar puts the events in, then hide the dates as above and write the label your story uses into the event name: "The Siege (Second Moon, Year 12)". The stand-in dates keep the events in order and set the gaps between them, and nobody reading the timeline ever sees them.
If your calendar needs finer spacing than years, stand-in months and days work the same way, and Supported Date Formats covers everything the date fields accept.