If you want to filter based on a time estimate range, use and advanced smart list filter:

The advanced Smart List filter option is at the very bottom of the list. Select it and then pick "matches" from the drop down options. 

Type the following into the input field:

>=~10m <=~20m &&

This matches tasks in the range of 10-20 minutes.

Don't forget to click "save" before closing the mini dialog. 

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