How long before I click 'No'

Yeah, true. But just give him time you never know, an emergency could of come up or something.

Things often happen in real life that get in the way of this. Wait until a week is up, and if you have not been in contact with the gifter at that point, open up a thread in support with all the necessary details.

Sometimes users have a busy schedule, that might delay them from checking there steamgifts account. You also have to consider other factors that could delay them like trouble with their computers, getting sick, and even life issues. Just wait the 7 days before marking it as not received. Good luck.