Timeline is wrong
By my calculations it was the 4th of August that Ron, Fred and George arrived to rescue Harry from Privet Dr in 1992. The book says that the day after his birthday Vernon installs the cat flap and has bars put on the window. He's allowed out morning and night to go to the bathroom. Then it says that three days later the Dursley's were showing no sign of relenting. That was the night that Ron arrived and if Harry was locked in on the 31st, then the bars were put on the window on the 1st and 3 days after that would be the 4th. Which also means that they would arrive at The Burrow on the 5th and the raids would have to change date as well.
If my math is correct, would someone change it please?