I realise that the OP means earliest in the day but another one I remember for being there a long time before the kick off was a Boro away match at Leeds United in the early 1980s when my dad and I went on the supporters club coach.
The coach left Ayresome Park at something ridiculous like 3pm for a 7.45 kick of in Leeds. The driver clearly didn't want to go through the centre of Leeds so went round by the M62 which felt like it took hours but we still got to Elland Road by about 5. The police then didn't want a load of Boro fans roaming around outside the ground so marched us straight into the away end, which in those days was basically a pen in the corner. By this point it was getting dark but it was about an hour before they even bothered to put the floodlights on and we were literally standing in the dark in an otherwise virtually deserted 1980s football ground.
When the game finally started it was a typical Boro away day at Leeds of playing well, getting into a winning position, getting a man sent off, giving away a dodgy penalty and losing.
Does anyone else remember that?