Internet requests from OS on startup

Does anyone know why MacOS Mojave is looking to connect to this website on startup? Uslax1-vip-bx-001.aaplimg.com

We blocked our internet for security purposes. On startup the whole computer slows down for up to 20 minutes as it looks for this website (sometimes also looking for Uslax6..., too)

Just wondering what it is before we make the decision to open it up to our computers.
If it's during (early) boot, it could be Secure Boot: https://support.apple.com/en-us/HT208330

I don't have any specifics about which servers that uses though. Later on, I suspect a gazillion connection requests will come from all kinds of daemons and apps.
It is an apple registered domain according to whois. Secure boot makes sense.
Internet requests from OS on startup
 
 
Q