If you've ever resented the colleague who makes a habit of slipping off home 10 minutes early or who refuses to make their mid-morning coffee a takeaway, you're probably onto something.

They could be working an entire week a year less than you.

We have all been reminded of the importance of a small number of minutes each day since unions representing public servants started staring down Commonwealth employers thinking about the possible lengthening of work shifts.

As Australian Services Union tax branch secretary Jeff Lapidos said, nine minutes a day meant an extra week of work a year or was equivalent to stripping someone of a week of leave.

The hearty debate about the importance of tiny portions of time each day - and how they accrue - is reminiscent of past reports of smokers costing their employers $3000 a year in smoko breaks despite the relative speed it takes to finish a fag.

Following news of the looming bargaining stoush in the public sector, a former senior public servant has warned lengthening shifts has nothing to do with increasing productivity.

Ex-Defence Department deputy secretary Paddy Gourley said more hours increased output, but had little influence on productivity, which was defined as the unit of output produced for each unit of labour.

In fact, he said the more hours an employee worked, the less productive they became toward the end of their shift. 

Mr Gourley said the federal government's push to link remuneration with productivity in the public sector was fraught with measurement problems.

"For most jobs in the public sector, it's very difficult to measure output," Mr Gourley said. 

"If you're writing policy in the Department of the Prime Minister and Cabinet (PM&C) or Treasury, how you measure output is anyone's guess."

He noted even productivity in call centres could be difficult to measure, simply because some customers were more difficult than others. 

"[Linking remuneration with productivity] is wrong headed and it can have perverse outcomes," Mr Gourley said.

"What bargaining ought to be about is doing what every other sensible employer does - the placing of rates of pay in a reasonably competitive position.

"Staff will be hard working and productive if they think they're being fairly treated."

The federal government's tough bargaining framework, which departments and agencies operate under, allows for no pay rises for 160,000 public servants in the next three years, unless their departments can prove wage increases are linked to productivity gains.

Cash-strapped agencies and departments will also have to show they can fit any pay increases into their dwindling budgets.