How to display a value in my text panel?

Hi everyone,
i a new in Grafana, and i want to display in a text panel a value called maintenance in my datasource (PostgresSQL).
I want to see in my text panel:
“Next maintenance in X hours” where X is my value maintenance (in hours).
I tried to create a variable which use my value like this:

I can see that is work in varaible options, because i can see “preview of values” my value.
But in my text panel, juste 0 is displayed.

How can i display my value maintenance in my text panel?

Thanks a lot for your answers.