Cache: When does the 15 days start?

Hi there,

On this page, I can read:

answers will be kept safely in their browser's local storage, for 15 days

My question is: When does the 15 days span start?

Does it start the time the respondent start the typeform?

Or does it start the last time the respondent loads or edits the form?

Thank you for your help!

Patrice