How do I insert relative date/time in notes?

I have a template that includes a custom span of dates. At this moment, in the body of the note all I can do is manually adjust it to the dates I need, but it would be nice to have Joplin do it for me.

More specifically, I want to have the first date be one day less than the current date and the last date, 7 days earlier. This is the template date format I am using now. It is the first line of the template:

Weekly review {{#custom_datetime}}Y.MM.DD-1{{/custom_datetime}} - {{#custom_datetime}}Y.MM.DD-7{{/custom_datetime}}

At this moment, the above template creates the relative date for the Name of note, but not in the body of the note:
Note name: Weekly review 2020.08.09 - 2020.08.03
Note body: Weekly review 2020.08.10-1 - 2020.08.10-7