Update the date field to the date & time of the node being updated I am sure that I am missing something very simple here, so I hope somebody can put me on the right track.

Use Case:


I have a simple content type "Article"
A date field of type: "Date and Time" is attached to this content
type.
Using any of "Rules" or "Business rules" module, I need when
updating a node of type "Article", to set the value of the "date
field" to be equal to the "date and time" of the node being
updated.


What is the right token that must be used ?

So far:

I have been trying for days with no success, I have tried to use the below token but yet no sucess:


[node:changed:custom:D-M-Y-H:i:s]
[node:changed:custom:D-M-Y H:i:s]
[node:changed:custom:D/M/Y H:i:s]
[node:changed:custom:DMYHis]


Any help PLEASE!!

UPDATE #1:

The real use case:

I am using the "Field Timer" module in my project which 
provides field formatters for core module Datetime to display timer or countdown as a formatter.

So every time the node is updated, I want to set the "date field" to the current "date and time" of the node being updated (+) 20 minutes.

For Example if the current date &amp; time of the node being updated is: 31/12/2018 15:00:00 so I want to set the "date &amp; time" field value to: 31/12/2018 15:20:00

So the countdown formatter will start from 20 minutes and down until 0 minute.

Thank you,
Nodes already have a 'changed' property that would track this. Any reason why you don't want to use that? You can use {{ node.getChangedTime() }} in a Twig template for the raw value, or you can preprocess the node and take the changed value and format the date to your need into a new variable for the template. This way you don't need another field and Rules and reduce a lot of overhead.