French phrase
Combien de temps ~ est-elle valable ?
Meaning
How long is ___ valid?
When to use it
This asks about the length of an item's validity. It is a somewhat polite way to check an expiry period.
Example dialogue
Combien de temps la carte d'étudiant est-elle valable ?
How long is the student ID valid?
Elle est valable un an.
It is valid for one year.