In the CB Nodelet, directly under the input field is a link to the Chatterbox FAQ labelled "How do I use this?". Included in the FAQ is the question "I came in late to a conversation. Is there any way to see older messages?" which mentions the last hour page among others. I find last hour of cb to be very useful and just like kcott have had it near the top of my Personal Nodelet for many years.