Heres my first entry for the 20SECONDS compo!
Its written in Blitz3D and using blitz own collision system. Its a bit slow, and will take longer than 20 seconds on any PC thats older than mine ( 6 years

)
I mite have a go at making my own collision system for it, so I can have more sand particles! and have it last 20s on any system

Its not a great simulation, and some of the collisions and accel is wrong, but it achive the effect

A zip file of the models and code is available for download, you will need the models to run the code.
the compiled exe is available here
Download