Is there a protection gap when upgrading from SEP 11 to SEP 12.1?

We are deciding whether to prompt the user to reboot when we push the SEP 12.1 upgrade to machines that have SEP 11.  If there is a protecting gap in the installation process, then I want to prompt the user to keep that gap as short as possible.  If there is no gap in protection, then I would consider not prompting the user and just waiting until the next time the user reboots.