I was discussing this word with a student @PauloA …you might be interested in the topic.
Die Tagesform ( the form of the day ), describes the performance ( physical and mental ) on a given day.
E.g.talking about a sport competition: Die Tagesform entscheidet über den Sieg ( The form of the day decides about the victory ).
I also remember hearing something is “tagesformabhängig”. In an old article for example:
…but is this word correct? Couldn’t find anything about it in the Duden. @SKrausser do you have any idea?