I would have no problems waiting.
If we are talking about parents... I think it should be mentioned that if kids have nothing to do, and have to figure out what to do on their own, they will be able to understand that there are sometimes where there is nothing to do. They will have the patience to wait. If parents are pulling their kids in 10 directions in a hurried pace, then they will probably feel rushed and have to eat it.
I also had roommates with older brothers and they always ate their food twice as fast as me (no brothers). They were afraid that their brothers would steal their food. They would probably eat the one marshmallow.
Now, to make it even more interesting for the adults... What happens if there is one girl (or guy if you are into them), but if you wait 2 hours, there will be two girls (or guys)... Would you wait?
(This test is more in line with the TFP)
