In a normal "bank run", the people are afraid that if they don't exchange the bad currency now at a discount, they will get a worse exchange later. But in this case there is a guaranty that waiting only 30 days they will be converted to dollars.
Hmm. Not exactly. Initially, this is true, but that's just an early part of the bootstrapping process. Further down the road, the total amount of GD will be greater than the amount of USD in our reserves. At that point, if everyone decides to sit on their GD at once, not all of it will convert because we would run out of USD reserves.
But this is what makes Greshm Dollar shine. If people don't trust their GD to convert to USD in 30 days, the only way for them to get rid of it is to spend it. By spending GD , they cause the GD's expiration to reset thereby protecting our USD reserves.