if a reboot is needed, it will either say it at the very begginng of the README or the very end under special instructions.
If the contents of the patch does not seem to touch the kernel, it probably will not need a reboot.
also look out for needing to be installed in single-user mode.
so yes, if it does NOT state a reboot is needed or having to be installed in single-user, install it whenever, preferably when the system is as close to idle as possible.