Track focus vs distracted time in study sessions.
The cost of a distraction is far more than its duration, because regaining task context takes several minutes afterwards. A three-minute phone check with a four-minute refocus costs seven minutes, so nine interruptions in a two-hour session consume over an hour. Reporting focus efficiency rather than raw session length is what makes the real cost of interruption visible.
Time lost
Minutes lost = distraction events x (average distraction length + refocus time)
Focus efficiency
Focus efficiency = (session minutes - minutes lost) / session minutes x 100
Studies of interrupted knowledge work report several minutes to fully resume the original task, and longer when the interruption is unrelated to the work. Two to five minutes is a defensible planning figure.
Removing the source rather than resisting it — phone in another room, notifications off, a single browser window. Willpower against an available distraction performs far worse than removing it.