The research described in the article was concerned with the possibility of determining time t8/5 using the Finite Element Method. The research-related tests involved a joint made of AHSS S960QL using the PAW-MAG method. Values of time t8/5 were compared in relation to characteristic zones of the joint and constant heat input values. Differences in cooling rates related to the diversified geometry of a joint and the asymmetric distribution of heat proved significant. The research involved the identification of possibilities offered by the Finite Element Method involving space modelling in the examination of the thermal history of any welded joint area. The comparison of the analysed manner of determining time t8/5 with traditional measurement and analytical methods revealed the significant advantage of the FEM consisting in the accurate and complete induction of a cycle in the entire cross-section of the joint in contrast with experimental contact and non-contact methods averaging the measurement on the joint surface or only in the weld axis. In view of differences related to time t8/5 reaching 1.5 seconds in the joint area and the very narrow range of the tolerance concerning the value of the cooling time of AHSS, the Finite Element Method involving the use of space modelling was recognised as a necessary tool when designing welded joints made of Advanced High Strength Steels.