Question : DNS - Slow to propagate - is this normal?

I updated a CName record to point a sub-domain hosted by my UK ISP to a domain in the US. I'm in North London, I can get on the site (12 hrs later), however my colleague in South London can't, nor can she ping the address, which I of course can, is this normal?

Answer : DNS - Slow to propagate - is this normal?

Yes it is normal.
Time of life for DNS records is fully configurable and sometimes may be quite long (many hours or even days).

Use nslookup instead of ping to resolve DNS issues. It gives you better information.