The Time Diary
Writing down what you did as you do it. The most accurate method, the most expensive, and the one most people try first and abandon.
The time diary is the reference method: a record made at the time, in your own words, of what you were doing. When this method moves from a personal experiment to a team process, time tracking software can reduce manual reconstruction, provided everyone knows what is recorded and the organisation keeps only the detail needed to answer the stated question.
How it works
A line per activity, with a start time. End times are implied by the next line.
Written as it happens, not reconstructed.
In whatever detail the question needs — "email" is enough for a coverage question, "email: three about the invoice dispute" for a specific one.
Paper works. A note app works. The medium matters far less than whether the entry is made at the time.
What it is good for
Precision about what actually happened, including the fragments.
Catching the things you would never remember: the eleven minutes looking for a file, the interruption that derailed the morning.
Billing, where a contemporaneous record has a standing that a reconstruction does not.
And the first honest look at a week, which for most people is the single most useful exercise in this subject.
What it costs
Ten to thirty seconds per entry, thirty to sixty entries on a fragmented day.
Plus the interruption cost of stopping to write, which exceeds the seconds spent.
Which is why almost everybody who starts a full diary abandons it inside three weeks, and why the abandonment is a cost calculation rather than a discipline failure.
Making it survivable
Run it for a bounded period — one or two weeks — with a stated end.
Round to five minutes. Minute-level precision costs more and answers nothing extra.
Do not categorise while writing. Write in plain words and sort afterwards; categorising in the moment doubles the decision cost.
Accept gaps. A line saying "no idea, 20 min" is more useful than an invented entry.
And keep the tool stupid. A notebook or one plain text file. Configuring a system is how the first three days get spent.
The backfill rule
An entry written more than about an hour later is an estimate, not a record.
Mark those differently — a question mark is enough — so you know later which parts are soft.
A diary where half the entries are reconstructed and none are marked is a diary you cannot interpret, and that is the state most abandoned ones reach.
When not to use it
When the question is "where does my week go" in general terms. Sampling answers that for a fraction of the cost.
When you know you will not sustain it. An incomplete diary is worse than a complete sample.
And when the activity is continuous and undifferentiated — six hours on one task produces one line and teaches nothing that a timer would not.
Reading it
Do not add up categories first. Read the lines in order, as a narrative of the week.
The findings are usually in the sequence rather than the totals: what followed what, where the day broke, what never got started.
Totals come second, and the note on categories explains why they are the part to do last.
What to check
Are your entries contemporaneous or reconstructed — and can you tell which?
Did you round sensibly, or are you recording minutes you cannot actually observe?
Is there a stated end date?
And have you read a day of it as a story rather than as a spreadsheet?
The rule that keeps it usable
An entry written more than about an hour later is an estimate, not a record.
Mark those with a question mark so you know later which parts are soft, because a diary where half is reconstructed and none is marked cannot be interpreted at all.
Worth keeping in mind
Read the lines in order as a narrative before adding anything up. Most findings are in the sequence rather than the totals: what followed what, where the day broke, what was started three times.
In short
Do not categorise while writing.
Write in plain words and sort afterwards: categorising in the moment doubles the decision cost per entry, and it is the decisions rather than the writing that make a diary expensive. For a complementary perspective on work, measurement or planning, consult Harvard Business Review.