Books like On Guard
William Lane Craig, Lee Strobel
On Guard is 288 pages, about 5 hours 17 minutes at 250 words a minute.
6 books to read next
How long each takes
The Case for Christ 6.3 h 
I Don't Have Enough Faith to Be an Atheist 8.2 h 
The Christian's Secret of a Happy Life 4.6 h 
Our Sufficiency in Christ 5.2 h 
The Gospel in a Pluralist Society 4.5 h 
The Reason for God 7.0 h Bar height shows length. Estimated at 250 words a minute.