Wording about LDAP sync time assumes the expiry is fixed at 1 hour

LDAP check expiry is a configurable setting which default to 1 hour. We have some user-facing explanatory text that always says 'after 1 hour' even when the expiry time is different, for example the 'Clear LDAP permission cache' warning modal.

I think we should use the actual expiry time in explanation text where possible.

cc @rdavila @JobV