This is an hourglass sand timer printed with natural translucent PLA for the "glass" which completely encloses the sand.
There are two versions of the glass; one with a narrower neck and the other wider. I used sand from a craft store, which isn't very fine, so I used the wider hourglass for the version you see in the video.
If you can find really fine sand, then try the narrow version.
Your time will vary depending on the size you print and the type of sand you use.
It turns out that in one direction the time is consistently 9 seconds and the other it is 12. It must be due to the texture of the print.
This thing was made on a MakerBot Replicator 2 using PLA.
Natural translucent PLA was used for the hourglass part.
You will need to print it with 1 shell and 0% infill.
Standard resolution seems to work the best.
The version you see in the pictures and video was scaled to 200%.
The critical step in this build is filling the enclosed glass with sand.
To do this, cold pause (sleep) the print of the hourglass at about 95% (you should also hear the tone of the printer change the last couple of layers before the top).
When paused, carefully pour a measured amount of sand into the glass, then resume the print.
You might want to do a dry run or two to get the amount right and to make sure that the sand you're using flows nicely through the neck.