single custom load does not work from the hard disk, it is in the floppy disk menu.

your answer, don't use the custom load, use composer load.

for the hard disk:
copy the custom style to the composer, using custom style copy in the composer menu. setup registrations for this composer, and save composer and 3 bank panel memories on the hard disk. Add sound memory or pads if you are using any other section in your registrations.
This will load in 2 seconds from hard disk.

If the custom style has been correctly created with registrations, pads, sound, tempo etc built in, save as a single custom style on floppy.
I get more than 120 single custom styles on each floppy disk.
This will also load in only 1 or 2 seconds from floppy disk.

There are many combinations of ways to find your personal optimum way of working.