If your system breaks, how long do you want to be down? How soon do you need your system back up and running? Whether it is a week, a day, an hour or one minute, whatever time you establish, that is your RTO or Recovery Time Objective. Think about what your business needs and you can come up with one component of disaster recovery/business continuity planning, your RTO. Next up, you need to start thinking about your Recovery Point Objective.
Smoke testing is a term used to describe the testing process for servers after patches are applied.
The process typically involves making sure servers are rebooted in the right order, making sure they have completely rebooted, restarting applications in the right order, and then testing to be certain everything is working properly when users return to work in the morning.
This typically takes 30 minutes per server, depending upon your environment.
PCs are not typically smoke tested, or if so, not all of them.