Looking at the way things have gone in recent times 20 August seems to be a rather important
20 August 2021: Martin Ødegaard, who had been on loan at Arsenal from Real Madrid, joined on a permanent deal worth £34 million and within a year was permanent club captain. On the same day goalkeeper Aaron Ramsdale joined from Sheffield United, for around £30 million
20 August 2022. Saliba scored his first goal for Arsenal away to Bournemouth. The win took Arsenal to the top of the Premier League for the first time since 17 January 2016.. Saka became the second-youngest player to play 100 times for the club in the Premier League, behind Cesc Fàbregas.
And we have a video from earlier days… Arsenal v Middlesbrough 20 August 1995