https://www.linuxquestions.org/questions/linux-general-1/grub-legacy-delay-of-more-than-2-minutes-loading-initrd-from-ext4-filesystem-4175599620/ up until my 2018-02-09 comment there might be relevant here. The initrd comment 1 refers to is 14135128 bytes. The subsequent dracut rebuild is 7451992 bytes and produces no apparent delay.