Holacracy Community of Practice Archive, 2015-2019 Community Holacracy Web Site

Great question. Hadn't thought of it before. : ) 

For Governance, I think the timebox fits within my interpretation of what "reasonable notice" means. You stop processing when the meeting time ends because "notice" only covered the time specified. 

For Tacticals, 4.2.3(e) says, "The Facilitator must attempt to allow time for processing every agenda item within the meeting, and in order to do so may cut off the processing of any item that’s taking more than its due share of the remaining meeting time."