“Last-minute” deals in travel and tourism services are very appealing not only to travellers but also for service providers. Timing and price are central to an optimization strategy for last-minute deals for both sides. This study analyses last-minute timing behaviour for self-catering customers and proposes to the supplier an estimation of the critical last-minute momentum (LMM) that is, the optimal moment for launching these kinds of deals. The data emanates from the largest self-catering accommodation booking platform in the Romand Valais in Switzerland, containing more than 154,000 transactions. The study focuses on the domestic market, that is the largest market of the platform consisting of more than 90,000 transactions. The results show that LMM estimation accuracy increases when the party composition is considered even though improvements are not homogeneous across seasons. For practitioners, the results clarify the timing optimization of last-minute campaigns. For scholars, the results demonstrate that last-minute behavior challenges traditional paradigms of the planning vacation process (PVP). This is an extended version of a conference paper entitled “When last-minute is really last minute” previously published in the proceedings of the Information and Communication Technologies in Tourism 2018: Proceedings of the International Conference (ENTER 2018) held in Jönköping, Sweden, January 24–26.