you can use the CAM-Subsystem from FreeBSD to control your disks.
list available disks:
camcontrol devlist
list disk-information about disk /dev/ada0:
camcontrol identify /dev/ada0
send disk /dev/ada0 to idle state:
camcontrol idle /dev/ada0
send disk /dev/ada0 to standby state:
camcontrol standby /dev/ada0
set the idle-timer to 60s for disk /dev/ada0:
camcontrol idle /dev/ada0 -t 60
set the standby-timer to 60s for disk /dev/ada0:
camcontrol standby /dev/ada0 -t 60