I have a flash dive that I use for installs, which gets rebuilt every time there is an update to the system. Yesterday, did the rebuild again. It took about 1 hours 30 minutes to complete. It's a USB 2.0 device that has been erased 25 or 30 times. Gets slower on every rebuild. (It's close to 'retirement'... )
So, nothing unusual with 30 minutes. Assuming the USB drive is still good, just wait it out.
Are you really installing the system to the flash drive? The usual goal with a flash drive is to use it to make a bootable installer from the OS X installer app. You can do that with the createinstallmedia command in the terminal.
Is that what you used?
Or easier, use the DiskmakerX app, which does a great job without entering anything in the terminal.
The time involved is about the same, as it uses the same commands, but DiskmakerX does that all in the GUI - and makes it pretty at the end. Nice drive icon, too.
The terminal commands that you used…
Did you use the createinstallmedia command as part of that?
You would remember if you did.
That would have been part of the link from that page, which shows you how to create the OS X bootable installer.
If you did create a good bootable installer - how long did you wait?
I would give it at least 10 or 15 minutes to finish booting up.
The other "option" that you have at the Option-boot screen, is to choose the recovery system.
Boot to that, then reinstall OS X from there (that should work, too.)
It will take significantly longer, because it will use your internet connection to download the OS X system files, rather than loading them from your USB stick. The result should be the same - it will just take longer.
If that is the command, as you entered it, then that explains the problem. you have the installer app spelled wrong....
this is in terminal:
sudo /Applications/Install\ OS\ X\ Elcapitan.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ OS\ X\ Elcapitan.app --nointeraction
If that is the command, as you entered it, then that explains the problem. you have the installer app spelled wrong.
your command SHOULD be:
sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/ElCapInstaller --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app --nointeraction
(see the / and space between El and Capitan.app - that's pretty important, and would prevent the tool from making your installer. You can try again with the corrected command, if you like. Should work this time.
Before you run that command, make sure that your target drive (the USB flash drive) is actually named ElCapInstaller
That is the name as your command wants it.
And, now it should all work.