No problem! You are right, subdomains usually are set up pretty fast, but caches (your browser, you computer; your ISP, etc.) still make resolving a “new” DNS entry a little dicey at first.
I’ve had luck “clearing” all that I can (can’t do much about an ISP ) and trying again. I use Firefox, and sometimes, even clearing the cache does not good until I close the browser - upon restarting it, I can often connect. Just a thought.