Question

The Headmaster said to the boys ,"You may not do your work well now and waste your time in doing unless things but you will repent later. "

Answer 1

Hey friend !

Here's your answer

================= >

In the question you haven't mentioned properly

But it might be the changing above sentence to the indirect speech.

Your answer for this :

The headmaster said to the boys that they might not do their work well at that time and waste their time in doing unless things but they will repent later.

We have changed :

You = their

May = Might

Now = That time.

# Hope it helps #

Answer 2

if you want to change into indirect speech then ans is
The Headmaster told the boys that they might not do their work well then and waste their time in doing useless things but they will repent later