I think the general wisdom is that you should be present for updates in case something unexpected happens, but you could certainly check for updates by adding this to root's tab:
Code:
0 3 * * * /usr/sbin/syspatch -c
syspatch(8) even mentions this very use case. Otherwise if you're dead set on applying the updates unattended, it doesn't have to be any more complicated than:
Code:
0 3 * * * /usr/sbin/syspatch && /sbin/reboot