HiFi Taq DNA Ligase is active over a range of temperatures (35-75°C) with greatly increased activity at higher temperature up to the Tm of the probe oligonucleotides used.  Typical ligations can be performed at 60°C. Ideally the reaction temperature should be chosen based on the Tm of the probes used, within a few degrees of the Tm of the probes used as calculated at the conditions of the buffer (10 mM MgCl2, 150 mM KCl) and the probe concentrations used.  The optimal reaction temperature for a given application must be determined empirically.