SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'c8a3a21b9bd5e6403a5f3d847600c06ddbf1490365bd004a4050ad7468232091' 
  AND token = 'BTZ/AqL/QvHblFNn6S6NYnJwD/XtWj7KWzfqJLUXg+8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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