Finding a good optimized timetable means playing around with the parameters and constraints.
In my opinion an UNDO (button) would be a helpful feature, since I could add / or modify some constraints and test the feasibility of the new timetable. Otherwise I can undo my last modifications and retry the timetable generation with other settings.
I conceive an UNDO function as it can be seen e.g. in MS-office showing a history of my last n modifications, where n ist the number of undoable steps.
The "history" of modification-steps would give me a good hint on what steps I could try otherwise.
Kind regards! :)
OK, I added this in the TODO, but I think I won't do it myself, at least in the near future.
You can use a CVS (git, cvs, svn, ...). I make timetables to my school with git, so can step back, see changelog, etc.