Yes this would be so useful. Asana/Click Up call this "time estimate". On asana when you select multiple tasks it displays at the bottoms the total time estimate for those tasks - it would be so useful! I am always too ambitious with my days, so it would help me realise what I've planned is not achievable. It also focuses my mind - so that if I've set a time estimate of 15 mins then I will really focus on achieving it.

If deployed in a similar way to Asana, I think it could be done without changing the approach to the UI too much.

This is also similar to another post that has over 700 votes
https://anydo.uservoice.com/forums/143587-general/suggestions/17707177-calendar-display-task-duration

Wow. This was first suggested 3 years ago in 2016. That's disappointing. Just downloaded this app and really like it but not having a simple field for completion time might be a dealbreaker. Seems like an easy feature to add and would help not having to think about it every time I open the app. Odd that you can plan your calendar but can't allocate time to a task.

Eat the frog principle.. Prioritize which is ugliest frog based on its estimated time and eat it first.
Please add feature to assign estimated time of completion

Make estimates for tasks could contribute to productivity. And you can more clearly planning your day according to your estimation times. It’s very important part of your efficiency.

Design examples in attachments.