Do I have to Install my game immediately after download?

I ordered a Sims 3 Expansion Pack on Origin and it's ready to download, but my SIms 3 base game isn't with me at the moment, so I cannot install the Expansion Pack right now. Can I download the Expansion Pack now so it is ready to install, but install it a few days later? Or will I have to re-download The Expansion Pack if I cannot install it immediately and if I turn off my computer or quit the Origin application?