Should you meditate with a timer? I currently do 15 minutes of meditation every morning. I use a stop watch. I see some people do more like 30 minutes. I was wondering how they kept track of time. Or is it roughly 30 minutes? I find that if I don't use a timer, I find myself thinking to myself during meditation, "I wonder if it has been about 15 minutes" and it seems distracting. I've tried meditation without a timer, but I guess the question is when do you feel you should cut it off?
Use a timer for the following reasons.  


Worrying about whether your session is done is a distraction.  A timer will free you from this.
A resolution to sit for X minutes may not work.
Even if the resolution does work, you could end up mistaking that for progress.  Don't laugh -- people mistake side effects of practice for the goals of practice. They'll ask if meditation can improve their grades, lead to particular hallucinations, etc...
There's no harm to using a timer. After all, group meditations also use a timer, it just happens to be a human who hits a chime.  There's nothing magical about people that makes chimes hit by them any less disruptive than those generated by an electronic device.