With the exception of kernel updates, you can update whenever you like without any restriction. Kernel updates require a server reboot so you must schedule them at a time that is convenient for you. If you don't mind rebooting the server during business hours, then there are no restrictions.
In my case, I was doing updates every week during business hours except for kernel updates that were scheduled on Saturday night and followed by a reboot.
More than this, with CentOS, you can update between minor versions without any problem. I did it for Zenoss Core v3.x from CentOS v5.3 up to 5.9 whenever a new one was released.