Doing a little search on [Yahoo, it can take hours for a new subdomain to propagate. That said, there are things that may make it appear that it is taking longer for propagation to occur. For example, maybe your ISP is caching DNS data and when you try to look it up initially it finds nothing. Your computer might cache it, too, so you might want to try [URL="http://search.yahoo.com/search;ylt=A0oG7l5TtKRQCnsAyrlXNyoA;ylc=X1MDMjc2NjY3OQRfcgMyBGFvA2FvBGNzcmNwdmlkAzcxTnQ5VW9HN3Y0NEczNG9VS1N6TGd3dXouQlA1MUNrc3pRQUNxdDQEZnIDeWZwLXQtNzAxBGZyMgNzYnRuBG5fZ3BzAzEwBG9yaWdpbgNzcnAEcHFzdHIDZmx1c2ggRE5TBHF1ZXJ5A2ZsdXNoIEROUwRzYW8DMgR2dGVzdGlkA1ZJUDE3MA--?p=flush%20DNS&fr2=sb-top&fr=yfp-t-701&pqstr=flush%20DNS"]flushing your DNS](http://search.yahoo.com/search;_ylt=A2KLtQ8us6RQawcAZCSbvZx4?p=new+subdomain+propagation&toggle=1&cop=mss&ei=UTF-8&fr=yfp-t-701).
In reality, I have not found any problems with long DNS propagation times for many years. In fact, just the other week I registered a new domain name and could access its parking page within a couple minutes of registering it. I keep my DNS with my domain name registrar, not with my web host. When I have created subdomains, I make the entry in cPanel to set up the subdomain, then go to my registrar's DNS and make the necessary changes. I can usually access the subdomain right away.
Next time you set up a new subdomain, try accessing it through a proxy like hidemyass.com if you can't reach it through your own browser. Then you can see how long propagation is really taking.