Hi @Julia_Forbes, we continue working on improving times, in fact we made shipped some very recently (see Timeline Show - Hide Sections, Tasks, Subtasks Sidebar Option - #3 by Emily_Roman, We’re replacing the current task pane on Timeline with a slide in task pane! and Section Dividers in Timeline - #4 by Emily_Roman 
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We’re aware subtasks on timeline are a popular request, we recently implemented them in Lists and Board project (see You can now see and action subtasks directly from your Project task list! and Subtasks in Board View - #30) so I’m confident we will implement them into other views like Timeline. I’ll make sure to keep you posted in the Forum as soon as I have an update on this topic!