I'm glad someone posted this advice. I've found this approach to be tremendously helpful in almost all aspects of my life. Instead of trying to finish a huge project all at once, I set my phone alarm for 5 min, 10 min, whatever I can muster, and work on the project for that time. Then, over the course of the project, I slowly ramp up the amount of time I spend in one sitting.
A very important addendum: if you've agreed with yourself only to put in 5 min, don't try to compel yourself to work on after the time has ended. Force yourself to stop. Otherwise, the 5-min rule will start to seem like a trick you use on yourself to do a lot of work, and it will stop being effective.
A very useful book that discusses the research showing that this approach works is this one. Although the book is geared toward faculty, much of the advice and research is generally applicable.