Half-lives ${T}_{1/2}$ of states in $^{95,97}\mathrm{Sr}$, $^{97,100,104}\mathrm{Zr}$, $^{106}\mathrm{Mo}$, and $^{148}\mathrm{Ce}$, which decay by delayed \ensuremath{\gamma} transitions, were determined by using a new time-gated triple \ensuremath{\gamma} coincidence method. Transition energy dependent effects such as time walks, time jitters, amplitude walks, and possible timing fluctuations of Ge detectors that contribute to the width of the time window were taken into consideration by comparing prompt and delayed cascades with similar transition energies. It is shown that the normalized triple \ensuremath{\gamma} coincidence counts of two prompt cascades with similar transition energies are similar. Also, it is observed that the real triple \ensuremath{\gamma} coincidence counts in the prompt cascades change systematically with the widths of the coincidence time window and the transition energies. Half-lives of states in $^{100,104}\mathrm{Zr}$ were measured for the first time. The half-lives of states in the delayed cascades were determined by using the prompt cascades with transition energies similar to those in delayed cascades. The half-life of the 2${}^{+}$ state in $^{104}\mathrm{Zr}$ is measured to be 2.0(3) ns. The B(E2$;{2}^{+}\ensuremath{\rightarrow}{0}^{+}$)(${e}^{2}\phantom{\rule{0.3em}{0ex}}{b}^{2}$) value and quadrupole deformation ${\ensuremath{\beta}}_{2}$ are 0.40(6) (${e}^{2}\phantom{\rule{0.3em}{0ex}}{b}^{2}$) and 0.47(7), respectively. $^{104}\mathrm{Zr}$ has the most deformed 2${}^{+}$ state among medium and heavy even-even nuclei, except for $^{102}\mathrm{Sr}$. This method is only approximately valid, but it is believed to be generally within 10% of the true value.