inclusion or omission of preposition

[MSmith]

Telling his student about homework for all days of a week (say the week from 21-8-17 to 26-8-17) a maths teacher says, " On each day of this week, your homework will be to solve in your notebook all the questions explained in class that day." Grammar we have learnt in school says that the preposition 'on' is usually omitted before 'each day'. I want to know, would it be wrong if it is used (as in the above sentence) and is not omitted?

[Alan]

Yes, 'on' is unnatural and unnecessary here.