Hi,
SEPM never requires system reboots. Only during some main maintenance activities, you need to restart the SEPM service and this is not a maintenance activity.
In case of problems, you might need to reboot the SEPM, it takes few seconds, your SEP clients won't notice it for hours. If you are worried that some other administrators are logged on the consoles and they could face a downtime, just send them a notification to not use the SEPM during a scheduled hour.