I know the first char is A and it's all upper alphanumeric. Is there a way to estimate how long a mid level single GPU using hashcat would take to crack it?
If the passphrase is exactly 8 characters long and the first character is known, then only 7 need to be brute forced. Assuming characters are 0‒9 and A‒Z, the maximum number of combinations is 367.
An AMD Radeon RX480 GPU can go through approximately 170,000 candidate WPA2 passwords per second. This means it will take around 367 / 170000 seconds at most to exhaust all possible 7 character upper alphanumeric passwords, and half that on average. This equates to an average of 2.5 days.
Note that higher-end GPUs and clusters of GPUs can crack such a password, and stronger ones, much more quickly. From Twitter, 8x 2080Ti GPUs can crack any 8 character password in ~2.5 hours!