How long does it take for my iphone to restore?

Its an iphone 4 and its restoring for about 6 hours now with the little spinning circle in the middle… What should i do?

If it's a jailbroken iPhone and you did the restore from the settings menu, that 6 hour circle isn't a good sign. I'd try holding the power and home buttons and see if you can get it to shut down. Then go into DFU mode.

unplug the phone
open iTunes
hold the home button on the phone
plug in the phone while holding the home button
keep holding until a picture of the usb cable comes up on the phone and iTunes puts up a message that there's a phone in recovery mode