I would say that if you've done any work in a productive direction, you've achieved something that day and can feel ok reporting your work in progress. Not all

I would say that if you've done any work in a productive direction, you've achieved something that day and can feel ok reporting your work in progress. Not all tasks may be able to be finished in a day, but you can make incremental progress on anything, even if it's only to find out a particular approach is infeasible.