I had a chat with Standa Graf from Red Hat about the idle3ctl WD disks utility, looks like some WD disks do actually follow the SMART/APM parameter and the spindown timeout can be changed using the standardized utility. Standa showed me a nifty trick to do this automatically and he claims it works for all his internal and external (USB) drives. I am gonna share the trick here:

cat >/etc/udev/rules.d/69-hdparm.rules <<EOF
ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="1", RUN+="/usr/sbin/smartctl --set apm,128 --set lookahead,on --set wcache,on --set standby,241  /dev/%k"

Unfortunately, my WD model (RED 2TB) does not accept the APM parameter and I need to stick with the idle3ctl utility:

# /usr/sbin/smartctl --set apm,128 --set lookahead,on --set wcache,on --set standby,242 /dev/sdc
smartctl 7.0 2019-03-31 r4903 [x86_64-linux-5.3.15-300.fc31.x86_64] (local build)
Copyright (C) 2002-18, Bruce Allen, Christian Franke, www.smartmontools.org

APM enable failed: scsi error badly formed scsi parameters
Read look-ahead enabled
Write cache enabled
Standby timer set to 242 (01:00:00, a vendor-specific minimum applies)

Thought it’s useful. Thanks Standa!