Time management is one of the harder parts of productivity. A to-do list might show you what needs to get done, but figuring out how long you need to spend on each task is tough. A Harvard Business Review article recommends dividing your tasks into three categories based on effort.
Basically, if your day is so busy that you're unsure how much time you have, you need to figure out which tasks matter and which don't:
Break down activities you do into three categories: invest, neutral, or optimise. “Investment” pursuits are areas where more time and a higher quality of work lead to an exponential payoff, such as strategic planning. Aim for A-level work here. In “neutral” activities, more time spent doesn't necessarily mean a significantly higher return. Attending project meetings is a good example. You don’t need to excel; a B is fine. “Optimize” duties are those where additional time leads to no added value and keeps you from doing other, more valuable activities. The faster you get these tasks done, the better.
It should only take you a few seconds to do. If your day is looking a little blown out with tasks, the three categories will hopefully provide the organisation you need.
Allocate Your Time and Your Effort [Harvard Business Review]