SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '198771b8675c03ca0424b63f5801b3ffc46cb8de657fb391863cd0f0f0c6b254' 
  AND token = '7q+OFFZnzakgh5VNXTLE3hKnk6T012Jvmw2X0RrEthI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00029

JSON explain

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