If the intended meaning is that you spend a short period of time learning or studying English, in this case 6 minutes, then 6 minute English as a title is perfectly correct. 6 minutes English doesn't make sense
It follows the same pattern as a 4 minute egg, a 5 mile run, or a 6 foot pole.
If you have a question about the English language and would like to ask one of our many English teachers and language experts, please click the button below to let us know: