Is there no way within the drive settings itself to keep it spinning on the RetroPie/Pi settings?
I haven't tested this but this might work!
You'll need to do most of this from the command line (difficulty: medium)
There are a couple hard drive power management programs that can be used on the Raspberry Pi to control how long before the hard drive spins down to save power and the life of the hard drive.
I wonder if the program hdparm will work for you. You could set the 'spindown_time =' to something like an hour (720) or 2 hours (1440). You basically find out how long you want measured in seconds and take that number and divide it by 5. So 2 hours is 7200 seconds (7200sec / 5 = 1440).
https://www.htpcguides.com/spin-down-and-manage-hard-drive-power-on-raspberry-pi/
