I think that homilies given by newly ordained priests often demonstrate their inexperience with public speaking and preaching. Given their typical younger age and inexperience, their messages often include discussion of Church History and/or teachings of doctors of the Church. I believe it is important to remember that these young priests are just coming out of the seminary, so much of their experience to speak of relates directly to things they learned.
With regard to length of homily, I don’t believe that time is of the essence; however, I think that experience in public speaking does bring with it a certain ability to keep the audience engaged while discussing a topic at length. Frankly, I believe that homilies given as a lecture do indeed have a tendency to lose their audience by about the five minute mark or so. It is a talented ordained that can keep their audience captive and engaged during long homilies. I recall as a youth serving at weeknight mass during lent we had a visiting Monsignor celebrating mass. While I don’t recall the topic of his homily, I do recall that he preached with such vigor that he kept the attention of the people for an excess of forty minutes - on a weeknight no less, and no one seemed to notice.
I believe that newly ordained could use encouragement and positive feedback as much as possible; and, constructive criticism as necessary, though perhaps the latter might be better delivered by the pastor or priest guiding over the newly ordained.
We should pray for our newly ordained that the Holy Spirit guide their homilies and teachings. I also think we should pray for ourselves and each other that we should approach the sacrifice of the mass with open mind and heart to receive the message being taught and focus less on the amount of time it takes to deliver the message.