It takes a few minutes to be ready to use terminal. If you are not using terminal, then stop the instance. This is how we save money (and save earth - In a sense, you don't use the electricity :) ). I personally don't want to wait, so I made a webhook to launch or terminate your terminal. You would see the curl command on Terminal -> Run, like below.
You can set up Clone job or use IFTTT. I'm using with IFTTT location service. For example, Enter the area where 100m away from office, then start terminal or Leave the area, then terminate the terminal.