Luckily, you'll only have to wait five minutes on average for a block to be found (blocks are one every ten minutes, so the expected delay until the next block is five minutes).
Upon reading it, I instantly felt that this was incorrect, and that the expected time until the next block is always 10 minutes (assuming the network hash rate matches the current difficulty).
If the blocks were generated exactly every 10 minutes, than it would be true that the expected time would be 5 minutes, but they're not.
So what's the real expected time? Please make a plausible argument for why it is so.