Quick Contact Expires After 68 Minutes

As described on this page:

http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/jabber/11_5/CJAB_BK_C9858CC7_00_cisco-jabber-features-guide/CJAB_BK_C9858CC7_00_cisco-jabber-features-guide_chapter_010.html

If you subscribe to the presence of a person who is not on your contact list (also called temporary presence subscription), the subscription expires after 68 minutes. After the subscription expires, you must re-subscribe to the person’s presence in order to continue to receive presence updates.

1. How can you find out if a user is in you contact list from javascript if I have his/her IM address?

Fetch method for any known-existing jabberwerx.Entity object. If the object does not already exist, `undefined` is returned.

That should tell you if the contact is in your EntitySet.  If you don't get 'undefined' as a result, that means that contact is in your roster. The "node" is optional, and you don't need to provide it.