"For a 'validate' method, I would expect a boolean return value."

Lets make it a 'get' method. :)
"In this validation, you are actually also falling back to a default
value. How about calling it get_timestamp"

It is now get_timestamp.
"How about using unless here? That might be easier to read."

True story.
Rename create_metrics_name to get_metrics_name for consistency
Instead of using "and" use "&&"
General cleanup.