You can add something like a meta refresh.
<meta http-equiv="refresh" content="5">
this header refresh page every 5 sec.
You need create custom web page in your <config-directory>/www/my_custom_web_page/index.html
For example:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta http-equiv="refresh" content="5">
<title>My custom web page</title>
</head>
<body>
<iframe src="https://you-iframe-url" frameborder="0"></iframe>
</body>
</html>
And just use custom page like iframe
- type: iframe
url: “/local/my_custom_web_page/index.html”
It’s actually partly documented here: Webpage Card - Home Assistant