Functional hourglasses would be neat.
They could function like candles/lamps, but with different messages. Holding and using it would reset its 'fuel' and 'light' it.
When used: $n inverts $m. The sand within starts to trickle to the bottom.
Last minute: The sand in $m has nearly all reached the bottom.
Finished: The last of the sand has reached the bottom of $m.