@ 3ogdy
Yes the Full System Scan is there, anything else you would have to create it. The problem being you can't just click on the Full Scan to change settings as it simply runs the scan.
Having created a new custom scan (use an existing scan option), name it, you should then be able to change the settings. They would need to be in the Custom scans section to be able to access further settings, using the three dots ... to see settings (attached images, for the quick scan which I have in the Custom section)
Again I really don't feel on-demand scan are necessary, but going further, if you are going to set them up to run at scheduled duration, you need to set it. How would you know what duration would suit them or even if they want a scheduled scan (surely you aren't going to ask each of them) ?
They would need to be in the Custom scans section to be able to access further settings, using the three dots ... to see settings