SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '5135c8fab956de6ac8bee2d20534746510a6a9a0da9ee15051a277e13baac27f' 
  AND token = 'S6wxmqNUjVeuztjCi+gR9oYWG5AckLfKifekl/43nUs=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}