How to modify the grub default timeout for CoreOS?

I am trying to reset the root password for my CoreOS machine for which I need access to the machine's grub. However, I don't see the grub at all and the machine boots up. I am on CoreOS stable (1010.5.0) and have added set timeout=15 to /usr/share/oem/grub.cfg and rebooted my machine but I still don't see my grub.

I came to know about this option from here: https://github.com/coreos/bugs/issues/302 but I see that this option was not meant to be permanent. If this has been removed, is there another way I can configure it?

PS: I am running the CoreOS machine as a VM on VMware ESXi, if that matters and whenever I reboot the machine and press any key I see the following console:

syslinux 6.03 EDD copyright (c) 1994-2014 H. peter anvin et al