Vishal you should be able to look at the transfer stamps between when they were transferred to the IVR extension and when they were transferred away inside your mod_xml_cdr.
Other than that you could write a variable like so at the start
<action application="set" data="ivr_${destination_number}_start=${strepoch()}"/>
and this at the end
<action application="set" data="ivr_${destination_number}_end=${strepoch()}"/>
But this makes it add more items to the XML-CDR and i think the best way is probably to just use the transfer times.