SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '71d56244b3d12b36f518b14643fb8da565902fb52b67da69a52d2322797d227f' 
  AND token = '2mULwIsUu3kb5uQCMhPtvkBetrndZO3i0YRyMrHStMA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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