Reinstall os x takes too long

You can download again whatever OS you've downloaded from the App Store before. You may possibly need a certain OS depending on exactly which Mac you have:

which MacBook Pro do you have: https://support.apple.com/en-us/HT201300

which MacBook Air do you have: https://support.apple.com/en-us/HT201862

which MacBook do you have: https://support.apple.com/en-us/HT201608

Then there's definitely something wrong with the hard drive 😟

If you can, take your Mac to an Apple Store or send it in for service > Mac Service Answer Center - Apple Support

A Mac running Yosemite has some age on it. That may be at least part of the problem.

Hi,

A Safe Mode boot deletes system caches that might help for Recovery mode.

Shut down your Mac while holding down the power button until the screen goes black.

Wait 10 seconds then follow these instructions.

To start up in safe mode:

1. Start or restart your Mac, then immediately press and hold the Shift key. The white Apple logo appears on your display. If you don't see the Apple logo, learn what to do.
2. Release the shift key when you see the login window. If your startup disk is encrypted with FileVault, you might be asked to log in twice: once to unlock the startup disk, and again to log in to the Finder.

To leave safe mode, restart your Mac without pressing any keys during startup.

Then try macOS Recovery.

macOS Recovery requires an internet connection preferably high speed broadband. The longest macOS Recovery should take is about 45 minutes to an hour tops.

Unless you have a clone or Time Machine backup, one way or another, Yosemite (it looks like that's what you want) has to be downloaded from the App Store. Instead of downloading directly to your Mac, another way to install an OS is with a bootable USB flash drive installer, created using one of these two methods:

http://diskmakerx.com/diskmaker-x-5-x-est-enfin-disponible/?lang=en

or

https://support.apple.com/en-us/HT201372

Hi,

You can't use the Cancel button, nor Command Q? The time estimate frequently starts high and fluctuates, but I haven't heard of one that high. Something appears wrong, quite possibly with your HD. You may want to do a hard shutdown (hold the power button down for about 10 seconds until the Mac shuts down), then boot into Recovery or Internet Recovery, open Disk Utility and run First Aid to see if it catches anything.

Then you can install any OS from about 10.7 (depends on which 2012 you have) all the way to the newest one, Sierra. Note that unless you downloaded the OS before (it will be in your Purchased tab in the App Store) and you don't want to install an OS that is too old (anything before Yosemite/10.10 is no longer supported by Apple), you'll have to install Sierra/10.12.