Five minutes is long enough to make a real start and short enough that it does not feel like a commitment. Put a task you are avoiding, such as an email or a form, inside a five-minute box and tell yourself you may stop at the alarm. Often the hard part was beginning. If you stop, you have still made progress, and if you carry on, press Reset and Start for another box.
When the alarm sounds, choose before you do anything else: stop, or run another five minutes. Deciding on the spot is easier than drifting on. For a smaller first step, the 2 minute timer is the same idea at a smaller scale, and the 10 minute timer suits a task that needs a longer burst.
This is a browser timer, so keep the page open and the sound on. A phone that locks its screen may not ring, and for anything important such as medication, use your phone alarm. The full set of controls is on the countdown timer.
A small routine makes the box work better. Write the task in the Label field before you press Start, since seeing the words on the display keeps you on one thing. Close other tabs that tempt you, and use Full screen if you share the room with others. If you finish early, stop and take the rest of the time as a pause, because the box is a limit and not a target.