They say it usually takes 48 hours to propagate fully, but I've always found that it works fine for me as soon as changes are made. If not they've never taken more than a few hours.
another question lets say i got my domain from planet domain and their dns are ns1.planetdomain.com and ns2.planetdomain.com, but I got a hosting account from hosters hosting and their dns are h1.hosters.com and h2.hosters.com, do I have to change the dns from the planet domain one's to the hoster's dns in my domain account?