The thing about a timer is that it defines time exactly. If you need to know when fifteen minutes is up you just set your trusty timer and in 15 minutes the ring tells you it's time. I used mine often in the computer lab. As the students came in they knew to go to the keyboarding program and begin their next lesson. Once all were seated and their hands were flying across the keyboard, I would set the timer for 10 minutes. They knew it was an implied promise-if they set right to work and spent the 10 minutes productively it would be over when the buzzer sounded. We would then move on to the portion of the class they would look forward to doing. They enjoyed Webquests, lessons in Excel, and learning how to prepare slide shows in Power Point.
Since I taught computers to the whole school, K-8, I found this short but continued method of practice very effective. I started using it myself during my planning periods. I always had trouble starting my emergency lesson plans when we returned to school each September. I started setting my timer for ten minutes-promising myself I could quit when it rang. Usually after several 10 minute sessions I would have enough completed that I could eliminate the timer.
I have continued to use a timer at home. I find that I'm more likely to focus and do a chore if I know there is a "promised" end in sight. I actually set it for 5 minutes and play beat the clock to empty my dishwasher. Think about your students and some of the tasks that a timer might help them complete. You might be giving them a tool to get them through those pesky jobs that few of us actually enjoy.
Timers come in a variety of fun shapes and characters. I always had several silly ones in my classroom. On the very rare occasion I had to give a time out it seemed to make it easier to bear on the part of the child.