how long does it take to restore an iphone via itunes

What do you mean it hasn't worked? What happens when you try?

If you're getting an error message, we need to know exactly what it says to be helpful.

How long it will take will depend on multiple variables... If you have not used that computer to update iOS on your phone, it will have to download the firmware file, which can take quite a while depending on your Internet connection speed. Then the firmware will have to be installed, which can take 1/2 hour or so depending on what model device you have, then the data must be restored and media re-synced to the device.

In some cases, it can take quite a number of attempts to get that to work. I have read some anecdotal evidence that it took a dozen or more tries before the device and iTunes would respond.

Did you try erasing with iCloud?

If you set up Find My iPhone on your iOS device or Mac, you can use iCloud to erase and restore it.

1. From another device, go to icloud.com/find.
2. If prompted, sign in with your Apple ID.
3. Click All Devices at the top of your browser window.
4. Select the device you want to erase.
5. Click Erase [device] to erase your device and its passcode.
6. Now you can either restore from a backup or set up as new.

If your device isn't connected to a Wi-Fi or cellular network, you can't erase it with Find My iPhone.

Hello,

Take a look at this article. Look under

"Put your device in recovery mode and set it up again"

If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support

Are you putting it into recovery mode?

Recovery mode shown here: