Can I download Mountain Lion and install it later?

Solution 1:

Yes, the App store downloads an installer for Mountain Lion and stores it in the usual spot - /Applications.

You should only need a network connection after installing to get updates, etc.. and not to run the installer outright.

Be aware that the installation process deletes the installer once you are done installing the OS, so you might make a backup copy of the Install OS X Mountain Lion program before you run it.

Solution 2:

There are a few complications to be aware of, and I think Apple is tweaking the download behavior. The answer above only works if you're an Administrator user, you haven't downloaded ML before, and you don't have an old copy of your install file in reach of Spotlight.

Also the download from App Store launches installer, so you have to quit to save it.

The best description of how to do this that I've found is here:

http://lifehacker.com/5929045/install-mountain-lion-on-as-many-macs-as-you-want-without-purchasing-additional-copies

Briefly (I'll do a blog post on this):

1. You need to do this from an admin account. I think if you use a non-admin account and quit the installer OS X deletes the download.
2. If you do this from an admin account Lifehacker suggests creating a fresh admin account for the download. I don't know if that's necessary, but I do know that if you quit the installer the installer does a Spotlight search looking for a previous Mountain Lion OS X Installer and then updates the previous installer. So you won't find it in Applications though the Installer icon will show up in Launchpad.