When changing the "details" field ("notes" in the API response) or Date/time field ("due" in the API response) of a task in the UI at https://mail.google.com/tasks/canvas does not change the "updated" time of the task and by extension the "updated" time of the tasklist.
Is there a way to change this behaviour to updating the update time no matter what change is made to a task? Could this be a bug? Seems odd to me that changing those fields would not count as an update to the task.
Modyfying a task in any other way results in the update time to be registered as expected. From my experience it appears that only those two fields don't behave as expected
Quote from https://developers.google.com/tasks/reference/rest/v1/tasks#Task
due string
Due date of the task (as a RFC 3339 timestamp). Optional. The due date only records date information; the time portion of the timestamp is discarded when setting the due date. It isn't possible to read or write the time that a task is due via the API.
So ... no luck so far, you can use time & also recurrence in tasks only from the web interface.