It's critical to distinguish between calendar time and labor time.
For instance, getting a visa to a different country might only take you 1.5 hours of labor time (fill out the documents, go to the consulate, wait in line, go back and pick it up later) -- but it might also take five days of calendar time, meaning you have to start five days before you need it.
There is a huge difference between a 10-hour task that you can "grind through" in a single 10-hour burst, and a 10-hour task that must be completed involving different people, at different times, with waiting periods between the actions.
When you're planning a project, it's useful to explicitly differentiate between calendar time required and labor time required. They work very differently.
Projects that require relatively low labor time, but high calendar time are particularly dangerous. They seem deceptively easy to complete, and often people start taking action on them too late to handle all the cascading steps in order.
Factor the calendar time and the labor time. Calendar time is particularly sneaky-dangerous, so identify the need for it and jump on it at a fast pace.