SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21cb2dad1007d75debff182ac9e6dccc251f4d84230e97512d07a760825df8af' 
  AND token = 'WCj9XfNCjY+L0yu8sQeCGCskrWlSHdZ+sDbSoyqKoOE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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