I'm not sure I fully understand your ask, but I'm hoping this may do the trick. The text mode below says if the actual completion date is past the planned completion date, display "Late", otherwise, display "On Time."
You can customize the Late/On Time terminology, but it should give you a framework to start with. Likewise with the displayname= line, you can customize what comes after the = sign.
group.0.displayname=Project Late vs On Time
group.0.valueexpression=IF({actualCompletionDate}>{plannedCompletionDate},"Late","On Time")
group.0.valueformat=HTML
textmode=true