If there are barriers to the elegant auto-summing-up-the-tree idea (e.g., developers believe people’s use cases don’t actually support it or whatever), I have a next-best suggestion: there could be designed some kind of “sum of estimated task duration” widget or ticker that the user could insert (preferably via a shortcut — by typing SUMhrs or SUMdays or something like that) on any chosen line, which sums and displays the total estimated durations of that line item and/or all its children.

Related: even outside of this coveted summing feature, I find myself wishing that there just was a quick way to enter estimated task durations to items, in the fashion you mention (by simply typing 2h, 45m, etc.) AHEAD of scheduling them. The current workflow forces you to schedule a task before giving it a duration, which is backwards in my mind. I want to be able to assign a task a duration before deciding where to schedule it.

Summing task durations as suggested is an amazing idea, but before it's even useful we need to be able to add task duration estimates in this quick fashion, in a way uncoupled from the scheduling process. If one had to wait until all tasks in a group were actually scheduled in the calendar (as the current workflow would dictate) to generate these kinds of project duration estimates, that would erase most of the planning benefit!

this is an amazing idea, would help me massively in personal and work tasks.

This is great!!! I always do this same method manually for every subtask, and then sum up every subtask time to add the total estimate to the parent list which they belong to. Some way of making this addition automatically would really rock!!!