DNS propagation can technically take up to something like 48 hours, though, generally it'll take at most about 2 hours or so, depending on the DNS servers provided by your ISP. If you set your own DNS servers and use something like Google's Public DNS (8.8.8.8, 8.8.4.4), this can be updated in just a couple minutes, at times.
Also, each record propagates on its own, so @ might start working before www, etc.