I am guessing that you submitted the transaction from an exchange 6 hours ago and it was only actually added to the Eth queue 20 minutes ago (that's what the explorer indicates). The exchange might be bogged down and only just submitted it. You should expect it to take another ~4 to 6 hours before it processes if the calculator I cited is accurate.

As long as you sent it to the correct address, I wouldn't sweat it. The transaction is not going to disappear, it will just take a while due to the low gas price.

It looks like you can resubmit the transaction with a higher gas price that should solve your problem. I have not looked at it carefully but this may be helpful https://www.reddit.com/r/EtherDelta/comments/72tctz/guide_how_to_cancel_a_pending_transaction/.

If you do resubmit with a higher gas price, try using like 80 Gwei so it is transacted very quickly!