"See you next summer!"
-- Harry, to the Dursleys as they watch him fly away in the car
Ron, Fred, and George wake Harry up in the middle of the night to take him to the Burrow. They use Mr. Weasley’s flying car to pull the bars off the window, and then they help Harry get his belongings and load them into the car. They manage to do all this without waking the Dursleys, but Hedwig screeches when she is almost left behind. This wakes Uncle Vernon, who bursts into Harry’s room and grabs Harry. But Harry holds onto the car and climb in, narrowly escaping. As they fly to the Burrow, the boys speculate on Dobby and his motives.
This event happens three days after Harry's birthday, which would be the night of August 3. He arrives at the Burrow, then, on the morning of August 4.
Here Harry leaves Privet Drive in a motor vehicle magically enchanted to fly. This is also how he first arrived at the Dursleys' home (in that instance it was a motorcycle). -BB
Channelling their father, Fred and George express their appreciation clever Muggle solutions to problems when they use a hairpin to pick a lock. -BB
When he doesn't receive letters from his friends during the summer, Harry thinks his friends don't care about him (CS1). When Ron doesn't get any mail from Harry, Ron worries that something bad has happened to Harry. (This is almost certainly due to their very different upbringings and their knowledge of each other's summer living situations.) -BB