Considering the example of libvirt documentation.

<clock offset='localtime'>
   <timer name='rtc' tickpolicy='catchup' track='guest'>
     <catchup threshold='123' slew='120' limit='10000'/>
   </timer>
   <timer name='pit' tickpolicy='delay'/>
</clock>
...

I know where this XML will be parsed. But I don't know where libvirt will pass clock/time settings to QEMU.