If you'd like to discover the deeper meanings of The Lord of the Rings, you will find it in the careful timing of events. Concerned with every little detail, Tolkien spent many hours getting the dates and their relationships just right. The result of over a year of work, this book shows what every significant character is doing on every day. It also adds other information from sources such as lunar calendars.
For instance: what is happening as Frodo and Sam reach the Black Gate?
1. The date is March 5 in the Shire calendar and February 27th on our modern calendar. The moon is 84% illuminated and growing brighter as it approaches the full moon. The bright moon makes it easier to travel at night, but also easier to be spotted by the Nazgûls, who are out tonight.
2. It has been 165 days since the hobbits left Bag End, nine days since the Fellowship of the Ring broke up at Parth Galen. Frodo and Same have been traveling with Gollum as their guide for seven days. In the night, a Nazgûl passes overhead for the third time, terrifying Gollum.
3. Before sunrise, Frodo, Sam and Gollum reach the Black Gate. They see armies enter, and Frodo decides to take Gollum's other way into Mordor. After dark, they travel in the wilderness alongside the road south.
4. Merry and Pippin have also been with Treebeard for seven days. The Ents have defeated Saruman at the Gate of Isengard and are enjoying the spoils of war.
5. After four days of riding with Théoden, Aragorn, Gandalf, Gimli and Legolas reach Isengard and discover Merry and Pippin.
6. The renewed fellowship leaves Isengard and camps at Dol Baran. An overflight by a Nazgûl causes Gandalf to order everyone to flee.
7. In the night, Gandalf flees south with Pippin, bound for Minas Tirith.
8. Based on a calculation of the Anduin River's speed, this is the night that Boromir's canoe-borne body enters the Great Sea.
Each of these events includes a link to where the details can be found in LOTR.