Subject: How long would it take an hourglass to expire on the moon?

This was a question posed by my physics teacher.  He doesn't know the 
answer, and he's left it up to us. Thus far, I would assume that since the 
moon's gravity is less than the earth's, it would take longer, presumably 
six times longer.  This doesn't seem a wholly satisfactory answer, since 
my teacher went to a physics convention, and apparently among ten or 
fifteen people couldn't find an answer. The only other thing I can think 
would affect the way it fell would be the change in interaction between 
the particles of sand since they weighed less. any help with this question 
would be greatly appreciated

Re: How long would it take an hourglass to expire on the moon?