hourglass(time)

This is an hourglass simulation.
Called without input arguments, it runs forever unless you close the figure. Called with input argument time, it will run once for the given period of time (in seconds).
Usage:
hourglass;
OR
hourglass(t);
You can expect more or less correct timing for t>20.
t is arbitrary, but i recommend to chose values between 30s and 600s.

Tillmann Stuebler, Dec 2016