I don't know if you want to to this dynamically, but this is the way for changing in web.xml:
<core:manager concurrent-request-timeout="15000" conversation-timeout="86400000" conversation-id-parameter="cid" parent-conversation-id-parameter="pid"/>
Sorry!! I was mistaken, is in components.xml
Is there a way to do it dynamically like the conversation.setTimeout()? And why is it that we can't use conversation.setTimeout()?