4 days just isn't long enough..What would you do?

Of course longer time is better. Is it possible to have a day off so that you will have enough time for your trip? I think this is a very important and exciting moment, and it's better to join it in person.

I love China

Well that was extremely rude and inconsiderate. How long have they known he was graduating? No, I would not rush to make plans to make it. Especially when you have to take a day off from work, that can't usually be done spur of the moment.
I would send him a gift with a nice card expressing my regrets that I couldn't be there. . .or not.

In many cases these last minute invitations get sent out for the express purpose of receiving a gift. As he's your nephew, you will be the one to determine if that is the case or not, but I definitely would not feel obligated to do the rush planning to be there.

Proper etiquette says that one should send invitations AT LEAST 2 weeks before an event such as a birthday party, and AT LEAST 6 weeks before an event such as a wedding or graduation. The only exception is for a funeral, for obvious reasons. So for your nephew or his parents to send the invitation giving you only 4 days to prepare for a trip was a serious violation of etiquette, and I wouldn't even bother to send a gift. Sounds to me like your "invitation" was merely a bid for a gift, so if I were you, I'd only send a nice card--no money, no gift.

I would have sent a card and a gift as well. What is that like 3 days notice. That is awfully short notice to give you for a 6 hours trip.

My IL's live 5 1/2 hrs from us...my husband could tell me we're leaving tomorrow and I would be ready to go before he finished the sentence!! Woohoo!!

However...with gas prices the way they are, and that it is a nephew that you likely don't know well except for holiday gatherings, and the fact that hubby can't easily get time of with such short notice (shame on them for getting the invites out so late) I would say send a gift.

I believe that I would just send the gift.. Most people understand all of the problems that you mentioned and a young person loves getting the gifts probably much more than getting the visit from the aunts and uncles.. It will be his night and he probably wants to share it with his friends..

I would imagine not. (No picnic.) With gas prices I think people are turning down more invitations like this and just sending cards with money.