A timeline or chronological reading plan is one where the reading follows the books and verses in the order they were written in time. IE when did it happen?
For example, reading chronologically we would start at Genesis 1 to 15, then the book of Job, then back to Genesis and follow the normal published order until the end of Numbers 15. Then we head over to Psalms 90 and back to Numbers 16 and so on.
This is a very useful reading plan in that it allows one to gain a true understanding of the order that biblical events and stories took place in history. It helps to put the stories into perspective and bring it to life. One can also study what was going on around various parts of the world at the same time to further relate where things fit together. Adding BC or AD dates to book headers would be helpful in this respect also, allowing readers to learn when individual stories or books were written and or set in history.