SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '15b21dccf3b2463ae9a63fa340a1b6f9ece8e6042a883ba17a473eaf9d3e6f55' 
  AND token = 'tSJY05xKRlhQB2GqqfTIS7BOfzZlXS7hX9uUsdli4nI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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