Thinking of time in 15-minute chunks instead of 1-hour chunks. It’s a cliché for everyone who wants to be a "productivity guru". Google it and you will find tons of articles talking about this. For me, there are two advantages.
First, I divided tasks into tinier subtasks. Therefore, whenever I get unexpected free time, I have reasons to persuade myself into working on those subtasks instead of slacking off and do relatively unimportant stuff.
Second, I have less time to waste in the chunks. When I want to procrastinate, I will use up all the time left in the current chunks no matter what. Therefore, if I’m thinking of time in 15-minute chunks, I have less time left in each chunk for me to waste.
Unfortunately, these two advantages only exist in theory (or in my fantasy). For example, in practice, I just procrastinated for more chunks instead of the time left in the chunk. However, this may work for you. You can still look up some articles and decide whether to try it or not.