Yes, there is a sort of inevitability in the way a sand-timer works, be it an egg-timer or an hour-glass such as was used on ships before the chronometer was invented.
The effect is particularly so when the bulb is nearly empty and though the grains are still falling at the same number per second the level in the funnel-shaped part drops ever more rapidly.
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From the profound to the practical....
Somewhere I have a sand-bulb egg-timer with a suction-cup for clinging to wall tiles.
It was part of a "water-saving" kit distributed by our water company, and gives sufficient time, about 3 or 4 minutes, for a shower including washing your hair.
I daresay many users cheated the system by turning it over to double the length of the shower... or just forgot about it after the novelty wore off. Mine did not stick to the tiles very well anyway.
The other two items in the kit were a w.c. cistern water-saver oddly called a Hippo, and an advice leaflet. The Hippo was a plastic, square, open-topped bottle that simply reduced the volume of water flushed at a time. It was designed for cisterns not fitted with dual-flush valves.
