>> Keep a log of your work. In fact, keep a log of everything you do.

> Set a timer to go off every 15 minutes

I realise this won't be a popular point of view with the folk who are always 'life-hacking' or what not, but my goodness that sounds mortifying to me.

I have worked in professional services too, and I had to bill for my time in 6 minute intervals, but I found it much easier to just switch between set of running timers when I changed tasks. No need to put together any timesheets at the end of the day, just note/submit the final times. I think a repeating 15 minute timer would literally cause me to go insane.

I'm all for people staying on top of their schedules, but I doubt that for most people the benefits of something like recurrent 15 minute timers could ever outweigh the costs (concentration, flow, mental health).