My google-foo leads to this:
https://discovery.endeavouros.com/installation/systemd-boot/2022/12/
where it looks like an edit to the 'timeout' variable in:
efi/loader/loader.conf
may be a possible solution.
DISCLAIMER: I use Slackware, and know nothing about systemd, etc....so tread carefully, backup, and research a bit before proceeding willy nilly!