It usually takes 24-48 hours for a domain to fully replicate changes, additions, or deletions across all name servers. For you to see the effects, however, all depends on your ISP. Updates may be within minutes for your neighbour, but may take up to a week for you or vice-versa.
The reason for this is the name servers for your ISP update at different times. For various ISPs it is quite possible for DNS take a week or more to update.
You might also get weird errors and unsuspected errors during the propagation period.
