Azure Firewall - whitelist AmazonSES IPs

Hi,

I am in the process of setting up Azure Firewall for a web app. Whitelisting the FQDNs of the SMTP servers we communicate with doesn't seem to be possible (at least not at the basic tier firewall that I am using), so I wanted to whitelist the IPs instead. From testing - it does seem to work fine, until the IPs change.

Now, I wanna do it by whitelisting the IPs as soon as they update. I don't want to have my script running 24/7, but rather linked to a schedule.

So, basically, my question is - is there a specific time at which these IPs get updated? How frequently does this happen?

Cheers