diff --git a/src/MDRequirementsSet.php b/src/MDRequirementsSet.php
index 5d39e3a..2965880 100644
--- a/src/MDRequirementsSet.php
+++ b/src/MDRequirementsSet.php
@@ -11,6 +11,12 @@ declare(strict_types = 1);
  */
 final class MDRequirementsSet {
 
+    // Newly created user account invites need to be accepted within
+    // the given timespan. If they are not, the account will be ignored
+    // and deleted.
+    // 60 * 60 * 24 * 6 = 518400. 6 days.
+    const MAX_AGE_AFTER_USER_INVITE = 518400;
+
     // Object images need to be at least 500 px wide
     const MIN_OBJECT_IMAGE_WIDTH = 540;
     // Object images need to be at least 500 px wide