"It only takes an hour" is the most expensive sentence in business.
An hour is nothing. An hour every Friday, for two people, all year, is something else. Here's the sum I use, and it fits on the back of an envelope.
The sum
Hours each time × people × times a year = hours a year.
For "times a year", I use 46 working weeks (a year, less holidays and bank holidays) or 230 working days. They're round enough to argue about and close enough to be useful.
So a report that takes two people four hours every Friday:
4 hours × 2 people × 46 weeks = 368 hours a year
That's roughly ten weeks of one person's full-time work, on one report.
Putting a price on it
Multiply by what an hour of staff time costs you, all-in. Salary is only part of it; employer's National Insurance, pension, holiday and the desk they sit at all count. If you're not sure, your accountant can give you a figure.
What the number is for
The number isn't what you'll save. Some jobs shrink to a few minutes; some only lose the boring half. What the number does is tell you where to look first and how much it's worth spending to fix it.
If a job costs you thousands a year and fixing it costs less than that, it's worth a conversation. If it costs a few hundred, leave it alone and look for a bigger one.
The time-leak audit runs this sum across every job you tick, so you can see which ones are worth the bother.