Here are the rules: All work must be done in blocks of at least 30 minutes.
If I start editing a paper, for example, I have to spend at least 30 minutes editing. If I need to complete a small task, like handing in a form, I have to spend at least 30 minutes doing small tasks.
See the conclusions here.
if you survive the annoyance, (…) your work will be of a much higher quality.