Editing GRUB2 timeout (standby time)

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Hello. I've been trying to change the default timeout seconds from 5 seconds to 1, but it's not been applied to the boot file itself.

What I've done:

sudo gedit /etc/default/grub

Then edited this line to be like this:

GRUB_TIMEOUT=1

Then updated GRUB2 with this command:

sudo grub2-mkconfig -o /boot/grub2/grub.cfg

But nothing changes when I reboot it.

Any ideas that might help?

Thanks in advance.