From the "Invitation" tab in the WAChat Settings menu, you can choose to display a chat invitation to your users.  Just set the title and message, as well as how long the user should be on a page before being shown the invitation.

From the "Chat" tab in the Settings, you can set how long the system will let a user wait for an Operator to respond to a chat request before that user is directed to the "Contact Us" form.  The default time is one minute.