Statistic card + helpers

Configuration
,
1

I have tried several options but none of them work… is it possible to use a helper as a source of origin for the start and end dates?

type: statistic
entity: sensor.consumo_casa_kwh
stat_type: change
name: Casa
period:
  fixed_period:
    start: "2024-12-16"
    end: "2025-01-16"

Something like:

 start: states('input_datetime.start_date')
2

Few if any of the built-in HA cards allow templates, but many of the custom cards do. Perhaps search thru GitHub using the HACS loader to find something that works for you.
In the mean time, there may be a Feature Request I think to add templates into cards in the Front End Feature Request Site so add a vote there.

In the short term, this is about the best you have using Ha tools to have adynamic window.