The "available from" option generally does a great job of preventing students from working on assignments too early, such as when instructors want students to see an assignment on their to-do list but still need to update the assignment before releasing it. However, I've gotten myself into a bind when I've set the available from date a little too optimistically early. Students then started taking the assignment, and I had to make a small number of them redo it after I made the required updates. One could argue I could better plan and manage my time, but unforeseen events still crop up and sometimes all we need are a couple of extra hours to get an assignment in order.
A more general availability lock in addition to the available from option would allow students to see an upcoming assignment in their to-do list while giving instructors the freedom to finish updating the assignment without accidentally allowing students to start the assignment early. I think a checkbox in the assignment edit page would work well. It would also help to show a "lock" icon in other locations in Canvas so both students and instructors can see the assignment is unavailable.
