This option currently exists in the Data Lab, but the users should not have to go there to edit the Timeline visualization. This is a guidance error.
We should add an option in the Timeline parameters list (along with Set Custom Bounds).
Good idea. Here you can see how it is done in datalab https://github.com/gephi/gephi/blob/master/DesktopDataLaboratory/src/org/gephi/desktop/datalab/ConfigurationPanel.java
11e09aa fix the issue