When you need to take a break. It's best to do it at what's called a break point in the task. Finish a section of what you're writing, or if you're working on a budget finish a complete portion of that budget before you start and switch to something else. We want to minimize this, this notion of the like, or an effect where you've got this unfinished task and you have to go back to it. Of course, if you still are writing that say that book chapter you're still working that budget but it will have less tension for you because you've come to a resting point in that task.