Even a 60 minute sermon will not make up for 6 days of personal negligence. Yes, 30 minutes is not a long enough sermon, but really it takes 6 days of personal investment to be maturing spiritually; to be personally in the Word for 6 days; to be praying personally for 6 days, Spiritual Maturity cannot happen by passively listening to a sermon, even if the sermon was 60 minutes long.
Showing up at the Charlotte Chess Center for a 60 minute lecture will not transform your chess game, you must go home and study the game for yourself, each day on a personal level of investment and attention. 5 minutes of Blitz chess will not improve your chess game, and 5 minutes of blitz devotions will not improve your Spiritual maturity.
Spiritual Maturity cannot happen by passively listening to a sermon, even if the sermon was 60 minutes long. Yes, God does use the preaching of His Word, but He brings His disciples to 7 days of personal investment to seek Him in prayer and Scripture. A pastor cannot "repair" 7 days of a persons own negligence with even a sermon, even if it is over 60 minutes long. In years past, I have enjoyed preaching long sermons, because I enjoy the Word.
Most golfers do not limit their golfing to 30 minutes, because they really enjoy golfing and time is not a factor. People do not go Snow Skiing and limit their time to 30 minutes on the slope. People enjoy shopping and all types of endeavors in which they are willing to put in more than 30 minutes into the activity; so likewise we should enjoy the Word of God.
But to my original point, it is wrong to think that even a 60 minute sermon could make up for someone's own personal negligence in seeking God daily.