The best advice one can give you regarding time management is to divide your time into small portions. Normally it is a period of nearly six weeks more or less so every day is important. Set your timing for research and decide how much time will you dedicate to research alone, increase that time by half and include writing in that time. Your first draft must be created as soon as you are done research and it is possible only when you are writing along with research. Dissertation takes more than one drafts so the time must be there to work on the drafts afterward.
Keep your focus on the task at hand. We do come across interesting stuff during the library trip and we are tempted to pick up that one book which is in no way relevant, we have to leave it for now and stick to the work. Similarly, the focus can be shifted due to a number of reasons and being overworked is one of them as well. Allow yourself to breathe in and a ten minutes break. A brain working continuously will be too tired to process the information and in that case, you are not using time well.
Plan your dissertation before starting the work. Planning will help you make a track of things you need to do. Allow these things relevant time slots and prioritize the work. Selecting a topic you already are familiar with will help you leaving out the initial process of understanding your topic. Prior knowledge will help you map places to visit to gather resourceful material. A huge amount of time is saved when the topic is already known and it also provides a finish to your work and gives it your personal touch.
Note keeping is very helpful to save time, if you have notes or important stuff highlighted, you will not have to go through books and websites to look for them. The other thing related to note keeping is being organized as much as you can. With everything sorted in its place, you can use the time you waste in sorting and looking for material in working on your dissertation. It will keep you calm and reduce stress.
You must be careful not to include irrelevant details which are not required and not related to your topic. You must know that this wastes time and is not needed. Instead, keep the dissertation simple and in easy language. Being good at time management is the skill that will help you along the way. An organized person manages time better than the rest so keep yourself sorted and focused and you can save chunks of time from here and there.