Context switching
Context switching is the cost of moving between unrelated pieces of work. The time lost is not the seconds spent switching but the minutes spent rebuilding the mental state the previous task required, which is why an interrupted hour is worth less than an uninterrupted one.
Also called: task switching, switching cost
Where it goes wrong
It is usually blamed on notifications, which are the easiest cause to see and rarely the largest. A calendar that alternates between four kinds of work all day imposes the same cost, quietly, with nothing to switch off.
Diarized schedules the work you already keep in a to-do app into the calendar you already use, and shows you why every block landed where it did.