Context:
At present choice of time estimates has to match pre-determined values. I find that some eg 20 or 90 mins are not included whilst others I never use eg anything 4 hours or more (if it will take this long, it probably consists of multiple actions and belongs as a project).
Ask:
Allow the user to create and/or select the values that appear in the drop-down list
(Presumably best achieved in the settings page)