If you predict that an unscheduled task is going to take 2 minutes, then you should not attempt it when you are within 5 minutes of your next scheduled task.
Your prediction may or may not become reality; things often take longer than expected.
In addition to that, other unexpected things always appear.
Attempting 2-minute tasks within the 5-minute zone of obligations (like meetings) almost always makes the obligation suffer.
Conversely, leaving yourself a minimum 5-minute buffer before an obligation – sometimes a longer buffer is even better – will allow you to be fully present, calm, and poised.
Matt Fried 