I’ve recently became aware of a time management technique known as the Pomodoro Technique. You time a period of work for 25 minutes, then take a short break, then do another period again. This helps you gauge the amount of work you’re getting done in a period of time, and is supposed to help with mental agility.

My friend uses Vitamin R as an app on his Mac to remind him of how much time he has left during a time period.