I use the free Powerpom app on the Windows Store. One of the key things for me when using a Pomodoro timer is... If I say I'm working on something for an hour, than anytime I get distracted, go to the bathroom, get a drink of water, I stop it.

If an "hour" of work actually takes me an hour to complete as opposed to an hour and 15 of real time, than it's a good day.