4 hours left in which to sleep.
You will not be able to sleep if you are anxious and you keep looking at the clock.
Your body can compensate with a loss of one night's sleep. In my IT career I did a lot of emergency 24+ hour jobs.
Here is what you can do: One hour before the interview, drink a cup of coffee, maybe 90 mins if you put sugar in the coffee. Although you may be tempted to give yourself a boost right before the interview, the sugar and caffeine will make you jittery and nervous.
Trust me - once the interview starts, the slight bit of nervous adrenaline will follow you through. Joke with them that you were nervous and didn't sleep. Good luck!
Thanks for the advice but I ended up skipping breakfast and didn't have time for coffee. I ended up wearing a tie for the first time in my life, it was the last thing I had time for before heading out.
Coffee would really have helped.