You'll need to wait between 24-48 hours for zone files to propogate. Sometimes less; it really depends on when you updated your zone files, and how often your ISP updates it's records with the main root servers.
the answer is *possibly*, Bashar was about right ...
if you change the nameservers for a domain you generally have to wait upto 72 hours before the new nameservers are used.
if you add to the records for a domain on it's existing nameservers then no waiting at all - i just added www5.oneofourdomains.co.uk
and it works *immediately* in a browser
if you change previous information has not been cached somewhere then no waiting.
if you change previous information has been cached somewhere then there *might* be some waiting dependant on the ISP that cached it - demon for example tend to remember the old locations and content of websites unless you bypass their local cache to get at the "real" content.
Most people that spout off about 48hours do so beacuse they dont understand the difference between NAMESERVERS and DNS records