Your e-tickets are valid for the date you enter when you buy them on the website
https://billetterie-cite-royale-loches.departement-touraine.fr/.
They are non-refundable (unless visitors are unable to enter the Cité Royale de Loches due to the site being closed in unforeseen circumstances). However, you can amend or exchange your tickets online as long as you do so before the date you originally chose to visit. You cannot amend or exchange your tickets after the date stated on your ticket.