The greyed out blocks are fine, but it would be nice, especially for non-regular time off (say a doctor or dentist visit, concert, etc) to be able to add a note to say what it is. I regularly override my time off if a student can only meet at xx time. Mostly, I know why I blocked it, but sometimes I don't. If we could add a note or title, it would be immediately clear that that particular time off is open for overwriting or it isn't.