What to do than?

I am currently struggling with one issue time management. Okay, it is easy be said, "plan your time", "focus on high priority tasks, delegate or reject the rest" etc. All sounds good to me.

But what happens, if you plan everything nicely, and according to schedule and than someone pops in between with something of crucial importance to the firm you are working for?

Sure, this happens, if you are a regional resource - people across the region can use you. And sure, they all have something important. And -big problem, if you are resource constraint, for whatever reason - like, you are a cost center, the firm downsized and everybody needs to handle more work etc. Is this then called time management in resource constraint times?