I also can confirm that grub
on my system is also doing a 30-second timeout, even though I have it set for 15 seconds:
GRUB_DEFAULT=saved
GRUB_TIMEOUT=15
GRUB_DISTRIBUTOR="Manjaro"
GRUB_CMDLINE_LINUX_DEFAULT="udev.log_priority=3"
GRUB_CMDLINE_LINUX="plymouth.enable=0 disablehooks=plymouth"
# Preload both GPT and MBR modules so that they are not missed
GRUB_PRELOAD_MODULES="part_gpt part_msdos"
# Uncomment to enable booting from LUKS encrypted devices
#GRUB_ENABLE_CRYPTODISK=y
# Set to 'countdown' or 'menu' to change timeout behavior,
# press ESC key to display menu.
GRUB_TIMEOUT_STYLE=menu