Hi @Jaffar Mohammad ,
Thanks for contacting Microsoft Q&A platform.
To update an existing container instance, we don't have "update" command, we will have to use az container create command.
You can find more info in the following document.
https://learn.microsoft.com/en-us/azure/container-instances/container-instances-update
Can you make a note of the scenarios and let us know in which cases it takes time & in which cases it takes long time etc. (Is that happening frequently?). So that we can help you in better way.
Hope this helps you.