It seems like there is no such template: “timeline_tooltip”. Where have you found such definition, possibly there is problems in documentation?
You could use “tooltip_text” template to set your custom text.
See article: docs.dhtmlx.com/scheduler/api__s … plate.html
If you want to show such text only on timeline view you could get scheduler mode with getState function.
See article: docs.dhtmlx.com/scheduler/api__s … state.html
You could save default template and use it if mode isn’t timeline.
For example: docs.dhtmlx.com/scheduler/snippet/f9f89bbe
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