Late-August was definitely when prices peaked.
Let's look at the 1980 Topps Magic/Bird RC:
PSA 7 - August price was $3,500+
Last one went for $1,850.
PSA 8 - August price was $6,500+
Last one went for $4,400.
PSA 9 - August price was around $25,000
Last one went for $16,722.
Baby, yes, I did spend $100,000 USD on basketball cards over the summer, but don't be mad at me. I have a good job and I can easily make this money back ... please baby ... look at me ... oh wait, I know! You want that pink Birkin bag? I can buy it for you right now!