Is it possible to completely disable Grub timeout?

Change GRUB_TIMEOUT value from 10 to -1, save the file and then run sudo update-grub2. Reboot and now you have infinite time to choose the OS.

While this works in GRUB, it doesn't work with BURG, and you'll have to change GRUB_TIMEOUT value to some large number like 120 seconds to wait before booting into any OS and run sudo update-burg to reflect the changes. Also note that this change must be made to file /etc/default/burg as BURG doesn't consider options set in /etc/default/grub

Setting timeout to -1 will make GRUB wait infinitely.

By that I mean that you will be required to manually select an entry and hit Enter before launching any OS.