Preliminary and weak — the general principle (attention wanes, breaks help) is supported, but 25 minutes is a reasonable default, NOT a proven biological limit.

Be honest here. The broad ideas behind Pomodoro rest on solid ground (the vigilance decrement, restorative breaks). The specific 25/5 structure has little direct experimental backing.

Biwer et al. (2023) found that systematic breaks made students feel more concentrated and motivated — a genuine benefit — but did not show that 25 minutes is optimal, nor that fixed breaks beat well-timed, self-regulated breaks on actual learning. Rigid intervals can even chop up a productive flow state. So: personalise the interval. Use the timer to start and to rest, but let the clock serve your work, not dictate a magic number.