I had it a while back. U only have to do it if u have a high bmi or like me my dad is type 2 diabetes. My appointment was at 8.30, u cant eat anything beforehand, i think from 12 midnight. I had mine at the doctors where they take a blood and i think u need to give a urine sample too then u have to sit there and drink a litre of lucazade which i cant stand anyway, but its even worse when you've had nothing to eat which made me feel a bit sick. U then have to wait 2 hours then go back and have another blood test taken. xx