Modification of boot time (grub timeout) is little different in rhel 7. Grub timeout is time to wait for manual selection of boot entry loaded by GRUB boot loader. This is useful for maintenance boot or to edit/modify boot entry In rhel 7 default grub timeout is 5 second.
In rhel 7 /boot/grub directory is not present nor /boot/grub/menu.list. In rhel 7 grub is modified with grub2 and we can use /etc/default/grub file to modify boot loader configuration.
It’s not recommended to modify any grub file in rhel 7 apart from /etc/default/grub.
Following are the default values from /etc/default/grub file.
To modify the grub timeout edit /etc/default/grub file and change the GRUB_TIMEOUT value to your choice I am changing it to 3.
If you change it to -1 then it will never boot the machine automatically it will wait for manual selection if boot entry.
Once you changed the value of GRUB_TIMEOUT run grub2-mkconfig command to take effect in boot configuration
Now just reboot the machine and check the boot timeout value.