update content_type_message ctm join node n on ctm.nid = n.nid set
ctm.field_message_recipientalert_value = unix_timestamp(date_add(n.created, interval 24 hour)),
ctm.field_message_senderalert_value = unix_timestamp(date_add(n.created, interval 24 hour));
From 12.2.10. UPDATE Syntax:
