Set the timer to 12 seconds

How to use the online timer

Back at the red postbox for a second run, you are already holding the letter by one corner as twelve seconds begin. The familiar route from the gate or parked bicycle may feel quicker now: cross the pavement, check that the stamp faces upwards, lift the flap and let the envelope fall fully inside. The repeat is less about rushing than seeing whether the same small task takes roughly the same time.

Posting the letter again makes consecutive countdowns useful because each run has a clear finish: the envelope passes beyond the postbox flap. Resetting between attempts keeps one result from drifting into the next, especially if another stamped envelope is ready. A delayed start, a stubborn flap or a moment spent checking the collection plate can explain why successive runs end differently.

Returning to the postbox during a British heatwave may change the action more than expected. Warm, slightly damp fingers can cling to the envelope, while a sunlit metal flap may be uncomfortable to hold. Keep the letter shaded until the run begins and use its dry edge, so it slides through cleanly rather than catching as the interval ends.