Yes, it is normal. You are installing from ports, so you are effectively building each application from source. This is the recommended way of installing applications on FreeBSD. When you run apt in CentOS, you are doing the equivalent of installing packages in FreeBSD. For more info on using ports vs packages in FreeBSD, see Installing Applications: Packages and Ports. Later, when it comes time to maintain (update) your ports, you may wish to look at the port portmaster.