For all the other users, here are the steps to follow in order to automatically set deadlines on Tasks.

1. From the task kanban or list view, create two advanced filters for each stage: Stage is equal to stage_name, Stage is not equal to stage_name.
2. In Settings > Technical > Automated Actions, create a new record for all the stages for which you want to set an automatic deadline:
3. Name: i.e. Set task's deadline to D+7 when stage = New
4. Model: Task

CONDITIONS TAB:

• Before Update Filter (pre-condition): retrieve the created filter "Stage is not equal to stage_name" in the list. If you want to add a deadline for the first stage (i.e. New), do not add this pre-condition in the automated action dedicated to the first stage, otherwise it won't work. Further, add "['date_deadline', '=',False]" in its post-condition filter domain in order to avoid an infinite loop. Indeed, without pre-condition, the post-condition would be always valid.

• After Update Filter (post-condition): retrieve the created filter "Stage is equal to stage_name" in the list.

ACTIONS TAB:

Create a new action:

• Object: Task

• Action type: Write object

Field mapping:

• Model: Task

• Destination: Deadline

• Type: Formula

• Value: time.strftime('%Y-%m-%d %H:%M:%S',time.gmtime(time.time()+7243600))

You can change the number of allowed days by replacing 7 in the formula (7 days).

Enjoy!