Where is the version that he practices diligently? I have not heard that.
Certainly in the famous hagiography of Tsang Nyom Heruka, the most well known 'biography', he does not practice.
Of course, Milarepa was not lazy as such, as we know from his biography. Rather, he interpreted the teaching on nonmeditation in a very literal way:
"Through this meeting I too have become one of those fortunate bodhisattvas who, having heard the teaching, do not even have to meditate on it. Triumphant, and thinking this way, without meditating, I spent the time sleeping."
I remember drawing attention to this story once in this forum, but the thread was deleted for reasons that were not clear to me. That is a shame since it is such a nice story, and very profound, in a way.