Can or May?

Can is determinate, if it is not otherwise qualified; may is not. In such a context, may has the same meaning as might, and is therefore conditional.

You can catch the train, there's time.

You may catch the train, if you leave for the station right now.

However, if can were qualified, it would cease to be determinate.

You can catch the train, if you leave for the station right now.

In casual speech the two sentences are interchangeable. I would not use the second sentence in writing a document.

From your explanation, I deduce that the right sentence to use is the one with "can." Am I correct?

Thanks again for your kind help.

It is possible for 'can' to refer to ability or permission. Which are you asking about?

Context:

Student to teacher: Is there a difference in meaning between the sentences 'ABC' and 'XYZ'?

Teacher to student: No. You can / may used them interchangeably.

In the context you provide, you can use either of them.