An in-beam method to determine lifetimes of nuclear states in the sub-nanosecond range domain with triple coincidences using an array of eight HPGe and five LaBr3:Ce detectors will be presented. The good resolution of the HPGe detectors allowed to select the decay cascades feeding the levels with lifetimes to be determined with the fast LaBr3:Ce detectors. Two measurements were performed at the Bucharest FN Tandem accelerator in order to demonstrate the capabilities of this method: a test measurement of the 7/2+ level at 205 keV in Cd-107 having the known half-life of T1/2 = 0.7 ns and the determination of the 3/2+ state at 367 keV half-life of T1/2 = 47 ps in Tl-199.