In September of 1532, Luther said in his Table Talks (2643a):
I hate a long sermon, because the desire on the part of the congregation to listen is destroyed by them, and the preachers hurt themselves.
A few months before in June he said (3137):
I cannot bring things together short and to the point like Philip and Amsdorf.
In the fall of 1533 he said (3422):
The sign of a good speaker is that he stops just when people are most interested in hearing him and feel that he has just begun. But when he is boring and people wait for the end of the speech, that is a bad sign. The same is true of preachers. When someone says: “I would have liked to listen longer,” that is good. When someone says, however, “He was prattling on and could no longer stop,” that is a bad sign.
In August of 1540 (5171a):
A preacher climbs up to the pulpit, opens his mouth, and then stops. That means a preacher must be called before he advances to the pulpit. He should preach carefully and be understood by all, and not burden his listeners with too much verbosity.
That same month it is reported (in 5171b) that Conrad Cordatus asked Luther: “Reverend Father, tell me in a brief way how to preach.” Luther replied:
First, you must learn to go up to the pulpit. Second, you must know that you should stay there for a time. Third, you must learn to get down again.
It is reported that this infuriated Cordatus.