Time spent in study is vital to a preacher. He must constantly study to be fresh and relevant. If you consistently study you will not usually struggle for something to preach. A pastor speaks to many of the same people for up to three times a week. This is a challenge. You do not want to be stale, boring, uninteresting or unknowledgeable.
A pastor may preach to people who are more educated than he is. Therefore he needs to apply himself to learning in order to identify with these people as well. This is not to say he must be an expert in other fields or that he needs to use big words, or preach above the heads of less educated people. People are not drawn to, or impressed by, ignorance!
A preacher should be a reader of good books. Books open a vast universe of knowledge to a pastor. A pastor often has to have a working knowledge of a huge array of issues, not just biblical.
Time spent is study is not wasted time, it is time well spent. You must also know when to pull away from study to spend time in prayer and to connect with people.
Study do show thyself approved unto God…