I been waiting for over 7 hours to install the update software Sur on my Imac! how long it takes ?

Normally an update or an upgrade will take about an hour to download, give or take. Then another 45 minutes to install, give or take. The times will vary depending on your internets speed and the speed of your computer. I am guessing that the reason you are unable to successfully install your operating system is because the installer became corrupted during the download. Put the installer file, if you have one, into the trash and do another download. If you were using Wi-Fi to do the download, don't. It's too much data for Wi-Fi. Instead, you need to use an Ethernet cable directly connected to your modem/router. If necessary, temporarily move your computer to do the download. And during the process, stay off the internet. If you are unable to directly connect to the internet, then be prepared to do multiple Wi-Fi downloads until you get a good one that loads. Good luck. I hope it goes well.