Microsoft Guru Eric Brechner discusses measuring "time on task" in his book "Hard Code". The discussion comes up during a section on Agile - Scrum. My guess is that it means "time spent to complete task X", but then he goes on to discuss time on task in terms of percentages by team. So I don't know how to make this logical leap.
In the Microsoft context, what exactly is "time on task"?
The daily stand-up meetings in Scrum are highly organized and collect useful data. The team organizer (Scrum Master) simply asks all the team members what they accomplished since yesterday (and how long it took) [...]
Tracking how long it took is my team's small contribution to Scrum at Microsoft. By adding this information to the burn-down data (how much is left to do), you can produce fantastic cumulative flow diagrams, measure time on task and work in progress, and better estimate team capacity. Typical time on task is around 42% for production teams; 30% for teams focused on communication--like mine--and as much as 60% for co-located feature teams.