When you have done a change to the zonefile for your domain name it can take up to 48 hours untill the change takes effect. Normally it takes according to TTL (time to live) that can varies between 1 to 4 hours as default.
If you want to change email provider or move your homepage to another host it is a good idea to lower TTL to 5 minutes so the change will go fast.
When changing name servers it normally takes 2 to 4 hours to take effect.