A working edition of the table of lunar mansions by Ibn al-Raqqām in his Shāmil Zīj, is used as the basis for an analysis of two cases of the use of lunar mansions for the purpose of timekeeping. One of them corresponds to al- Judhāmī (an Andalusian author of the end of the 12th c. and beginning of the 13th c.) who uses the mediation of mansions to establish the beginning of dawn and obtains excellent results. The second author is the well-known Moroccan muwaqqit al-Jādirī (1375-c. 1416) whose data on the lunar mansions are also analysed.