Something I like to do is to know what the focus of your timeline is before writing it. In my sadly defunct "Prodigal Sons" the main focus was on political developments in the state of Wisconsin. Then, I created a second circle, which was developments in the United States. Finally I had the rest of the world, which I didn't delve into too much as it took attention away from my main topics. So, in you're case, you might want to focus mainly upon the Indian Ocean and then deal with the rest of the world only where it would impact your main stage.
Another strategy is you can pic a distinctive section of the world, and expand outwards where and where it makes sense. In a second timeline I am working on, "Amalingian Europe" I started with the POD of Theodoric the Great having a son and the Goths remaining a major force in Europe. Here, rather than focusing solely on Western Europe, I have branched out to detail other sections of the world in a fair amount of detail. Usually, when I do this, I release several chapters relating to a particular region or topic. For instance, I knew that a Gothic West would have a major impact upon the Byzantine Empire and the Middle East, and so I released a series of chapters detailing that region. I also knew that the British Isles would be impacted, and so there are a few chapters dealing with Britain and Ireland. The nice thing about this is that you can create a vague notion of how you want things to go in each part of the world, and even reference it, and can then turn back and explore each topic in more detail once you have done your research and firmed things up.
In general, another thing you can do to make it seem more realistic and detailed it to form a general outline of where things are going and then drop vague references and foreshadowing for later events throughout. For instance, lets say that you are doing a timeline where the CSA wins the Civil War. You have a vague idea that the Confederacy falls to a Socialist revolt in the 1920s and that, after an alternate WWI, Britain goes fascist. You don't have all the details worked out yet, but that's where you want things to go. Well, reference those events in your narrative; have a section from a textbook entitled "The Abortive Republic: The Confederate States from Birth to Death" or do a chapter were a character is presenting a historical paper at a conference in Russian-occupied Iran. This draws the reader into the world, and by hinting at future events, builds anticipation and also helps to create a sense of a more fleshed out, realistic, world (it also can help you, as an author, by forcing you to not wander too far afield).
Does that help, a bit?