Experimental results of “time-delayed interferometry” with nuclear resonances at KEK are reported. Mossbauer nuclei were used as a cavity for X-rays in these experiments. Various interference effects were observed on a macroscopic scale with the “perfect crystal” interferometer. The property of coherence and the combined system showed some characteristics of collective nuclear excitations, e.g., absorption of photons without the reduction of the detection probability, the phase information transfer, and spontaneous emission with phase relation. Interferometry with a large optical path length, i.e., 4.2 mm, was accomplished with a wave-front division type X-ray interferometer. An interference experiment with a vibrating resonant scatterer exhibited quantum beat oscillations in the time domain. Interferograms with samples of different thicknesses revealed a remarkable phase shift of π in the time evolution, which is induced by the dispersion effect at the nuclear resonance. A future perspective of time-delayed interferometry is also presented, e.g., for temporal phenomena in nuclear resonant scattering. Time-delayed interferometry has established a new field of X-ray optics, which can be of help for fundamental, nuclear, and solid state physics.