The 25-minute interval is a default, not a law. If you keep hitting your stride right as the timer rings, your intervals are too short, stretch them to 45 or 50 minutes. If 25 minutes feels impossible to sit through, the task is usually the problem, not the timer, so break it into a smaller first step.
A rough guide: 15 minutes for very distracting environments, 25 for general tasks, and 45 to 90 for deep, creative work. My Deep Work lets you set any length, so experiment and keep what fits your attention.