Bitcoin Client Download Time

[bithoya]

Newbie here...

I downloaded the Bitcoin QT client for Mac. I heard that it was supposed to take a long time, and it has been a while (like 20+ hours) for my client to synch with the network. My internet is slow so I'm not very surprised. Anyways, I was wondering if I have to wait for it to synch everytime I open the client, or is this a one time thing? Thanks!