Mindjoy can draft a mark scheme for a question, which is usually faster than writing one from a blank box.
Generating one
Open the lesson from My Library and click into the question you want to work on.
Under the question you will find Mark Scheme and a Generate Mark Scheme button. Write the question first, set the marks, then click Generate.
Read what comes back and edit it. A generated scheme is a starting point, not a finished one, and it is your edit that decides how the whole class gets marked.
See also How long answers are marked.